TRIUMF: Canada's national laboratory for particle and nuclear physics

Annual report scientific activities, 1988 TRIUMF Oct 31, 1989

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TR IUMF0RIUMF LIBRAR,'ANNUAL REPORT SCIENTIFIC ACTIVITIES 1988CANADA’ S NATIONAL MESON FACILITY OPERATED AS A JOINT VENTURE BY:UNIVERSITY OF ALBERTA SIMON FRASER UNIVERSITY UNIVERSITY OF VICTORIA UNIVERSITY OF BRITISH COLUMBIAUNDER A CONTRIBUTION FROM THENATIONAL RESEARCH COUNCIL OF CANADA OCTOBER 1989TR IUM FANNUAL REPORT SCIENTIFIC ACTIVITIES 1988TRIUMF4004 WESBROOK MALL VANCOUVER, B.C. CANADA V6T 2A3E X IS T IN GP R O P O S E D REMO!HANDlFACILI1SERVICEBRIDGEPROTON HALL EXTENSIONSERVICEANNEXEXTENSIONH POL/ IO NTE>LINGITY\  INTERIM  ^-RADIO ISO TOPE  LABORATORYBAT HOBIOMEDICALLABORATORYi SOURCEARIZEDSOURCENEUTRONACTIVATIONANALYSISTHERMAL MESON HALLNEUTRON SERVICEFACILITY ANNEXCHEMISTRYA NNEXMESON HALLM9(TT/u)20(m )MESON HALL EXTENSIONP)BL2C BL1A (P)42 MeV ISOTOPE PRODUCTIOt CYCLOTRONA(P) /BLIB(P)FOREWORDThe year 1988 was marked at TRIUMF by a number o f highly significant events. While the basic research program and applied program continued to thrive, the year saw the start of two very exciting new projects: the KAON Factory Project Definition Study (PDS) and the design and construction, under contract with Ebco, o f a 30 MeV cyclotron. The main topic of this report will be the achievements of the basic science program. This foreword will serve to introduce the PDS and 30 MeV project as well as the move toward incorporation o f TRIUMF as a legal entity.The PDS is an $11M study, financed jointly by Ottawa and Victoria, and is expected to be completed by the end o f 1989. It is a major step forward toward a decision by Canada to fund the construction o f the KAON Factory at TRIUMF. The PDS includes many important technical studies aimed at reducing cost and other uncertainties related to the KAON Factory. It also includes consultations by Canada with its potential foreign partners in KAON. These are aimed at eliciting firm statements o f their intent to join Canada in supporting initiation of this major project. There is then every likelihood that KAON will be fully launched not long after the completion o f the PDS. TRIUMF is very fortunate to have Alan Astbury, on leave from the University o f Victoria for this purpose, as the leader o f the PDS.Another major new venture for TRIUMF in 1988 was its work with Ebco to build a commer­cial 30 MeV cyclotron. Ebco completed contract negotiations with Nordion late in the year to produce such a cyclotron, designed expressly for isotope production, by June 1990. TRIUMF has the nation’s best expertise for cyclotron design and construction and has an appropriate technology transfer agreement with Ebco under which TRIU M F’s knowledge and personnel are being extensively used for this project.Significantly, the PDS and the Ebco project together will involve several dozens of TRI­UMF’s staff. The cost recovery from these projects, however, permitted normal TRIUMF salary increases to occur in 1988. With the prospects for KAON, the work overload and the need to maintain the full science program of the existing TRIUMF facility, it is clear that interesting times lie ahead.Also in 1988 the first steps were taken toward legal incorporation of the TRIUMF Joint Ven­ture. As a national laboratory for Canada TRIUMF takes pleasure in noting that the founding four universities (Alberta, Victoria, Simon Fraser and British Columbia), which still carry legal and financial responsibility for TRIUMF, have now been joined by three additional universities (Montreal, Toronto and Manitoba). The universities are, initially, associate members o f the project but already have representatives at the TRIUMF Board o f Management. With the University o f Regina expected to join by March 1989, TRIUMF will include universities repre­senting every province west o f the Maritimes. The incorporation o f the TRIUMF Joint Venture is likely to take several years to complete.The TRIUMF Board was pleased to welcome Dean Robert Miller o f UBC as a new member replacing Vice-President Peter Larkin who has served the Board so ably for many years.B.P. ClaymanChairman, Board of ManagementTRIUMF was established in 1968 as a laboratory operated and to be used jointly by the University o f Alberta, Simon Fraser University, the University o f Victoria and the University o f British Columbia. The facility is also open to other Canadian as well as foreign users.The experimental programme is based on a cyclotron capable o f producing three simultaneous beams o f protons, two o f which are individually variable in energy, from 180-520 MeV, and the third fixed at 70 MeV. The potential for high beam currents -  100 pA  at 500 MeV to 300 fiA  at 400 MeV -  qualified this machine as a ‘meson factory’ .Fields o f research include basic science, such as medium-energy nuclear physics and chemistry, as well as applied research, such as isotope research and production and nuclear fuel research. There is also a biomedical research facility which uses mesons in cancer research and treatment.The ground for the main facility, located on the UBC campus, was broken in 1970. Assembly o f the cyclotron started in 1971. The machine produced its first full-energy beam in 1974 and its full current in 1977.The laboratory employs approximately 363 staff at the main site in Vancouver and 18 based at the four universities. The number o f university scientists, graduate students and support staff associated with the present scientific programme is about 575.C O N T E N T SINTRODUCTION ......................................................................................................................................................... 1SCIENCE DIVISION ...................................................................................................................................................  3Introduction ....................................................................................................................................................................  3Particle Physics .............................................................................................................................................................  5Spin correlation parameter A yy in n-p elastic scattering .............................................................................  5Radiative muon capture with the TPC  ............................................................................................................ 5Muonium-antimuonium conversion ...................................................................................................................  3Test of charge symmetry in n-p elastic scattering at 350 MeV ....................................................................9The Lamb shift and hyperfine structure in muonic atoms ..........................................................................10Radiative muon capture (RM C) on hydrogen ................................................................................................ HMeasurement of the flavour-conserving hadronic weak interaction .......................................................... 13Study o f rare K  d eca y s ......................................................................................................................................... 15Measurement o f spin-dependent observables in the pp elastic scattering from450 to 700 M eV /c ...................................................................................................................................................181 ftMeasurement o f A —*■ n j  ...................................................................................................................................... 10Nuclear Physics and Chemistry ................................................................................................................................21Polarization transfer in the pp —► dn reaction ................................................................................................ 21Multi-nucleon modes in pion absorption on 4He ............................................................................................21Spin-transfer measurements in 7r +  <f —+ p + p ................................................................................................... 22Measurements of the spin-flip probability Snn for inclusive inelastic scatteringof 290 MeV protons from 44Ca .......................................................................................................................... 25Single-pion production in np scattering ...........................................................................................................26Few-body physics wdth the ird break-up reaction ..........................................................................................26Absolute 7r± p differential cross sections at low energies .............................................................................. 27Spin response o f magnetic dipole transitions in 156Gd and 164Dy ............................................................27Cross sections and analysing powers for the 3He(p, 7r+ )4He reaction in the energy rangefrom 250-515 MeV .................................................................................................................................................28Measurement o f the cross section for H(7T~, tt+tt-  )n very close to threshold ....................................... 29Research and development studies with TISOL ............................................................................................ 31Spin excitations in 208Pb ..................................................................................................................................... 32Polarization transfer in inelastic proton scattering from 160  ..................................................................... 34Spin-flip probabilities with the (p, n) reactions ..............................................................................................37Analysing powers in ir^p elastic scattering between 98 and 263 MeV ......................................................37The A (7r, 2tt)A' reaction above threshold .......................................................................................   38Pion-proton bremsstrahlung ................................................................................................................................40Excitation o f the 10.957 MeV 0 ~ ,T = 0  state in lsO by 200 and 400 MeV p ro to n s ...............................40Measurement o f np —> dn° cross sections near threshold .............................................................................42Gamow-Teller transitions to isospin triads in A=6,12 nuclei studied by (n ,p), (p ,p ') and(p, n) reactions at 280 MeV ................................................................................................................................ 42Measurement o f B + (G T ) for 76Se using the (n ,p) reaction.... ..................................................................... 44Knockout o f deeply bound nucleons ................................................................................................................. 44The 20N e(n ,p )20F reaction at En =  198 MeV ............................................................................................... 45irN N  resonances .....................................................................................................................................................46Spectral function o f p+n  in 6Li ..........................................................................................................................47A study o f the spin dipole resonance in 40C a(n ,p )40K ................................................................................ 48Investigation o f single particle spin dipole transitions in 15N (n ,p )15C reaction ................................... 49Isovector giant resonances in 238U (n,p) and 181Ta(n,p) .............................................................................49Study o f the 3H e(n,p)3H reaction .....................................................................................................................50Enhancement o f the 5 = 1 , T —0 nuclear response in pion scattering ........................................................ 51Measurement o f the angular distribution o f the spin transfer parameter D ls in PP —* dir+ .............53Analysing power zero crossing angles in np elastic scattering below 300 MeV ..................................... 53Measurement o f analysing powers in low-energy 7rd elastic scattering .....................................................53True absorption o f low-energy pions by nuclei and the pionic atoms anomaly ..................................... 54ir+ p  total cross sections at low energies ........................................................................................................... 55Search for spontaneous 7r° d e ca y ........................................................................................................................ 55Search for dibaryons ..............................................................................................................................................56Research in Chemistry and Solid-State Physics ....................................................................................................57Muonium in micelles ..............................................................................................................................................57pLCR spectroscopy o f free radicals ................................................................................................................... 57LCR of muonated radicals in m icelles...............................................................................................................60pSR studies o f sub- and supercritical fluids .................................................................................................... 62Muon spin rotation studies o f dioxygen and ethylene adsorbed on a silicasupport ...................................................................................................................................................................... 63/i+ SR in high temperature superconductors ................................................................................................... 64Chemistry o f pionic hydrogen .. ....................................................................................................................... 68The effect o f conduction electrons on the diffusion o f light interstitials................................................... 69Theoretical P rogram .....................................................................................................................................................71Introduction .............................................................................................................................................................71Nuclear structure ................................................................................................................................................... 71Proton-induced reactions and scattering ..........................................................................................................72Few-nucleon processes ........................................................................................................................................... 72Meson physics ......................................................................................................................................................... 73Electron scattering ................................................................................................................................................. 76Symmetry breaking ................................................................................................................................................77QCD and quark models ........................................................................................................................................79Electroweak interactions ...................................................................................................................................... 81Other topics ............................................................................................................................................................. 82Experimental Facilities .............................................................................................................................  84Experimental support ............................................................................................................................................84Data acquisition software ...............................................................................................................................84Detector facility ................................................................................................................................................84M W PC facility ..................................................................................................................................................85Meson hall ................................................................................................................................................................ 85M9 channel upgrade ........................................................................................................................................ 85QQD spectrometer ........................................................................................................................................... 86Beam line IB ..................................................................................................................................................... 86Proton hall ...............................................................................................................................................................87TISOL ..................................................................................................................................................................87Dual arm spectrometer system/second arm spectrometer ................................................................... 87Targets ...................................................................................................................................................................... 88Experimental facilities engineering .................................................................................................................... 89APPLIED PROGRAM S, TECHNOLOGY k  ADMINISTRATION DIVISION .........................................91Applied Programs ...................................................................................................................................................91Introduction .......................................................................................................................................................91Biomedical program ........................................................................................................................................ 9142 MeV cyclotron facility ...............................................................................................................................92Radioisotope processing (Nordion) ..............................................................................................................94Positron emission tomography (PET) ........................................................................................................94TRIM  and beam line 2C ................................................................................................................................ 96Site Services and Administration ....................................................................................................................... 98VlllSite services .......................................................................................................................................................98Safety p rogram ..................................................  98Building program ...................................................................................................................................... 100Design office ................................................................................................................................................101Machine shop ..............................................................................................................................................101Planning .......................................................................................................................................................101Administration ................................................................................................................................................102A ccou n tin g ...................................................................................................................................................102Administrative data processing ............................................................................................................. 102Materials management .............................................................................................................................102CYCLOTRON DIVISION ........................................................................................................................................104Introduction ...........................................................................................................................................................104Beam production ..................................................................................................................................................106Cyclotron systems ................................................................................................................................................107RF .................................................................................................................................................................... 107Magnet ............................................................................................................................................................ I l lInflector and correction plates ...................................................................................................................I l lProbes and extraction systems ................................................................................................................. 112Developments ........................................................................................................................................................ 112Beam quality ................................................................................................................................................. 112rf studies .........................................................................................................................................................112Data analysis and display .......................................................................................................................... 113Ion sources and injection system ..................................................................................................................... 113Primary beam lines ............................................................................................................................................. 115Control sy stem ...................................................................................................................................................... 116Projects .................................................................................................................................................................. 117Alternative extraction system ...................................................................................................................11730 MeV cyclotron for isotope production .............................................................................................. 118Operational services .............................................................................................................................................118ACCELERATOR RESEARCH DIVISION ......................................................................................................... 122Introduction ...........................................................................................................................................................122Beam development ...............................................................................................................................................123Cyclotron ........................................................................................................................................................ 123IS IS ................................................................................................................................................................123Central region .............................................................................................................................................124Outer region ............................................................................................................................................... 124Extracting H° by laser stripping .............................................................................................................124Alternative extraction .............................................................................................................................. 125Orbit dynamics for the TR30 cyclotron 125Primary beam lines ........................................................................................................................................126Beam line 1A ..............................................................................................................................................126Beam line 4A ..............................................................................................................................................126Secondary channels ........................................................................................................................................127M9 channel ..................................................................................................................................................127M13 channel ............................................................................................................................................... 127M15 channel ................................................................................................................................................127Beam line diagnostic development ...................................................................................................................127Computing services ..............................................................................................................................................128KAON Factory ..................................................................................................................................................... 130Orbit dynamics ............................................................................................................................................... 131Proton injection and extraction ................................................................................................................. 133Beam transfer ..................................................................................................................................................134H_ injection ..................................................................................................................................................... 135Beam stability ................................................................................................................................................. 135Longitudinal dynamics .................................................................................................................................. 136rf cavity development .................................................................................................................................... 136Magnet power supplies ..................................................................................................................................137KAON FACTORY PROJECT DEFINITION STUDY ................................................................................... 139Introduction ........................................................................................................................................................... 139Science workshops ................................................................................................................................................139Experimental areas .............................................................................................................................................. 139Targets .....................................................................................................................................................................140Magnet development ............................................................................................................................................140Kickers .....................................................................................................................................................................140Beam pipe and vacuum system .........................................................................................................................142Systems integration ..............................................................................................................................................142CONTROLS, ELECTRONICS AND COMPUTING DIVISION .................................................................. 143Introduction ........................................................................................................................................................... 143Electronics services .............................................................................................................................................. 143Project team A ..................................................................................................................................................... 143Project team B ..................................................................................................................................................... 144Data analysis centre (DAC) ...............................................................................................................................145CONFERENCES, W ORKSHOPS AND MEETINGS ..................................................................................... 148ORGANIZATION .......................................................................................................................................................150APPENDICESA. Publications ......................................................................................................................................................153B. Users group .......................................................................................................................................................162C. Experiment proposals .................................................................................................................................... 165xIN T R O D U C T IO NLife is rarely normal. 1988 has been a year at TR I­UMF in which the present TRIUMF program has moved forward strongly. The experiments which car­ried that forward momentum are chronicled in this an­nual report. But there was much more.The “more” which enlarged the normal life of TRI­UMF was the advent o f the Project Definition Study (PDS) for the KAON Factory and -  secondarily, but still very important -  the work toward the 30 MeV commercial cyclotron. The latter project involved the use o f TRIUMF staff and ideas, under an appropriate Ebco-TRIU M F technology transfer agreement, toward the rapid production o f a new 30 MeV, 400 pA cy­clotron for isotope production. Both the PDS and the Ebco project receive only cursory attention in this re­port although they correspond to very significant mile­stones in the historical trajectory of TRIUMF.The significant move toward KAON with the PDS can be regarded as part o f TRIU M F’s manifest des­tiny. It may be useful here, where we begin the record of the substantial scientific achievements o f TRIUMF in 1988, to provide a perspective for where KAON re­sides in the psyche o f TRIUMF. The emergence of the present TRIUMF facility into a world-class laboratory has accompanied a dramatic transformation of the ba­sic ideas about what lies at the heart of matter. The ideas pertain to the basic building blocks o f matter -  the three generations o f quarks and leptons -  and to the unification o f the description of nature’s four fun­damental forces. These new ideas, taken together, are called the “standard model” . It has provided a remark­able synthesis o f everything we had learned about sub­atomic physics. In turn, it has led to urgent new ques­tions (and the corresponding new facilities) seeking to refine the standard model or go beyond it. TRIUMF has achieved its position in the world because of the effective way in which its experiments have responded to the issues o f the standard model. Read on, in this annual report. The KAON Factory builds on the ex­isting TRIUMF program and seeks to augment it in a way which will retain centre stage, at TRIUMF, for decades to come, in the important sequels to the stan­dard model. Therefore, the present TRIUMF program, although now in full flourish, very naturally bridges into the new era which KAON will bring.Amidst these future hopes and dreams the present science flourishes. The versatility o f muons, which are one o f TRIU M F’s most important particles, continues to provide surprising new science. Long ago TRIUMF had, among the world’s meson factories, played its fair role in exploring the important science questions asso­ciated with normal muon decay and the various possi­ble rare decay processes of muons. Such normal muon pursuits will be revisited in the future as new genera­tions of detectors allow significant gains in our knowl­edge. In the meantime, now, we find an astonishing variety of processes involving TRIU M F’s muons. As recorded in this report they include, among others, the muonium-antimuonium conversion search for the strength o f interaction constants, the very fundamental search (seriously attempted for the first time) for ra­diative muon capture in hydrogen and muon spin rota­tion studies o f radicals, fluids and high-temperature su­perconductors. Muon physics at TRIUMF seems very likely to prosper for a long time.Equally buoyant are the nuclear physics programs involving medium-energy proton and neutron beams at TRIUMF. Every “user laboratory” such as TRI­UMF thrives only if it retains user demand. User de­mand is maintained if and only if the laboratory con­tinues to provide new world-leading facilities. In the proton hall TRIUMF did this, a few years ago, with its high-quality beams and spectrometers and especially with its CIIARGEX facility which, for the first time anywhere, provided for the study of (p ,n ) and (n ,p) reactions and, moreover, enabled these over the en­tire medium-energy regime. The burst o f experiments which followed continued through 1988 as recorded in this report. In the near future TRIUMF plans to pro­vide a second-arm spectrometer and also high-intensity (several pA ) polarized beams which will extend the in­terest of the nuclear physics in the proton hall for many more years.Almost everyone loves theorists (sometimes even more than is necessary). Although TRIU M F’s theory staff is small, it is very productive in new ideas for the field. Good physics involves a healthy symbiosis be­tween theoretical and experimental ideas. At TRIUMF the theoretical work is greatly augmented by a large group of young theoretical research associates and alsoby many short-term and long-term visitors. TRIUMF has attained a considerable reputation for its work on medium-energy processes and also for the work of Woloshyn and his collaborators on QCD and quark models.There are many unsung heroes at TRIUMF who de­serve to be serenaded. These include the TRIUMF op­erators who, short-staffed, achieved record cyclotronproduction. A warm chorus should be given to Alan Astbury and his colleagues who have marched bravely into the work o f the PDS. Certainly also a signifi­cant cheer should be given to John D ’Auria and John Vincent who, without significant resources, have perse­vered with bringing TISOL into a position for impor­tant new science.2SCIENCE DIVISIONINTRODUCTION1988 has been a very exciting year indeed in terms o f the science output for our laboratory. The inter­est in our facilities remains very high as measured by the number o f new proposals submitted (43) or the total number o f shifts requested (2000) on our beam lines. The Experiments Evaluation Committee has rec­ommended that about 50% of the requested shifts be granted, and the cyclotron was able to deliver a record number o f 366 mAh for the year. A total o f 75 experi­ments received beam this year.In particle physics, a number o f groups are studying the properties o f the leptons and possible extensions o f the standard model. At TRIUMF Expt. 304 has now improved its limit for the conversion process of muonium to antimuonium, using a very original radio­chemical technique. The process is not observed and an upper limit on the branching ratio o f 2x l 0-6  was deduced, which for the first time tests this hypothet­ical interaction at a level below the Fermi coupling strength.A group from TRIUMF in collaboration with Prince­ton and Brookhaven National Laboratory is searching for the very rare second-order weak process K + —+ ir+ i/T'. The detector was completed early in 1988 and the first engineering run (14 weeks) took place. All components and, in particular, the TRIUMF parts are performing according to expectation, and the analy­sis o f this run should also yield results on K7rp+ p~, K  n j j  as well as determine the magnitude o f potential backgrounds.The studies o f weak interaction in the quark sectors are conducted in two major experiments at TRIUMF. Experiment 452 will search for the radiative capture of negative muons in ultrapure hydrogen in an attempt to deduce the induced pseudoscalar coupling constant gp. A new detector which includes a large angle pair spectrometer based on a drift chamber similar to the one built for Expt. 787 at BNL has been built, and is now in early stages o f commissioning.Before its retirement the time projection chamber was used in experiments on radiative capture in nu­clear targets, which yielded values for gp in 12C, 160  and 40Ca which are not confirming the large renormal­isation effects in nuclei previously claimed.Another major effort is mounted by the Manitoba group to measure the parity violation in hadronic re­actions, namely p-p scattering at 222 MeV. The in­strumentation development and engineering program is continuing, and good progress has been obtainedwhich should lead to a firm proposal soon. If the feasi­bility o f the experiment is confirmed, this experiment would determine the weak /^coupling constant.The Manitoba group is also pursuing detailed stud­ies o f the nucleon-nucleon system and has measured the spin correlation parameter A yy in n-p scatter­ing at three energies. These measurements are cru­cial in determining better phase shifts solutions for the parametrization o f the interaction and are discriminat­ing amongst several potential models. The inclusion of these results in the databases will greatly constrain the phase shifts analysis. Similarly the group is planning a second phase to the study o f charge symmetry in the n- p elastic scattering process at 350 MeV. Together with their previous results at 477 MeV, this measurement will pinpoint the contribution o f the p°-u  term.The nucleon-antinucleon system has also been inves­tigated via the measurements o f spin-dependent ob­servables at LEAR. A group from TRIUMF has col­laborated in Expt. PS 198.A number o f groups were involved in the search for bound systems containing a pion and two nucleons. These were searched for via the study o f 7 transitions from a tt~ d atom to the neutral form n°nn or n~pn (Expt. 511) and in proton-induced reactions using the MRS (Expt. 478) but so far none have been found.In nuclear physics, the program has continued to ex­ploit the superb facilities provided in our proton hall. We are delivering variable energy proton beams with any spin orientation and, together with the polarimeter at the medium resolution spectrometer, a complete set o f polarization observables is accessible. We also pro­vide a unique facility (CH ARGEX) to study isospin properties o f nuclear transitions.Now that we have a reasonable understanding of the elementary nucleon-nucleon force, the effort con­centrates on refining our knowledge o f the p-nucleus interaction. Spin observables are particularly sensitive to small amplitudes, and using appropriate transitions one can get at very specific pieces o f the nucleon- nucleus force. When coupling this information with the selectivity o f the pn, np reactions in terms o f isospin, a detailed tool is then available. A good example of this type o f work is presented in the report for Expt. 432 where specific transitions to stretched states 4“  in 160  are used to filter out the isoscalar part o f the interac­tion and the spin transfer coefficients are measured to get the separation o f the spin-orbit and tensor com­ponent. Similarly in Expt. 459 the 0+-0~ transition in3160  is used to get at the tensor component.Using the CHARGEX facility isospin components o f the interaction are selected, and searches for gi­ant resonance (Expt. 486), extraction o f the Gamow- Teller strength distributions L—0 continued. A new high pressure gas target was commissioned and three experiments took advantage of it.The pion program in the meson hall is now mov­ing from the study o f the elementary processes (7r± p and 7r± d) to pion-nucleus physics, and several exper­iments were devoted to pion absorption mechanism studies (7r4He absorption, (7r, 27t) reactions). The ele­mentary amplitudes for 7rp and 7rd reactions have now been pinpointed to very high precision and with con­sistency. The comprehensive studies o f polarization ob­servables in the 7rd system are now almost completed. Complementary studies o f the inverse reaction chan­nels (np —► dir0, pp —► dir+ ) add to the knowledge of the parametrization o f the 7r-nucleon interaction which can now be used to investigate the more complex 7 r -  nucleus system. We are now entering the phase where nuclear physics can be studied via this new probe, the pion.The techniques o f muon spin resonance (pSR) have allowed major advances in solid physics and chemistry. pSR has made an important impact on the character­ization o f the new high Tc superconductor materials. The phase diagram mean ordering in temperature and the oxygen content has been systematically explored, and it has been shown that a region exists where bothsuperconductivity and spin glass order coexist. Two and possibly more p + sites have been identified. //SR has made unique contributions to the field, and a large demand for these facilities has materialized.In chemistry both muon spin rotation (pSR) and muon level-crossing spectroscopy (pLCR) have been used to elucidate the role o f micelles in the reactivity of muonium atoms in various solutions (Expts. 371, 447) and for the study o f organic free radicals (Expt. 398). Experiment 450 focused on the transitional regions be­tween low pressure vapours and condensed media and set out to resolve the fate o f the missing muonium sig­nal. It is concluded that both spur and hot atom pro­cesses are involved.The theory group has more than ever played a key role in the scientific program, and apart from its own personal interests, the group has made decisive con­tributions to our experimental program: Elucidation o f the P n  amplitude puzzle in ird scattering, radia­tive muon capture on the proton, spin correlation in muon capture on 3He, determination of the neutron spin-dependent structure function, charge symmetry breaking in n-p scattering, parity violation in p-p scat­tering, charged Higgs effects in rare decays. The in­teraction between theorists and experimentalists is ex­tremely effective and plays a key role in the formulation o f the experimental program for our future activities (K-factory). The large number o f visitors attracted to TRIUMF is a measure o f the quality and the scope of their research.The contributions on individual experiments in this report are outlines intended to demonstrate the extent of scientific activity at TRIUMF during the past year. The outlines are not publications and often contain preliminary results not intended, or not yet ready, for  publication. Material from these reports should not be reproduced or quoted without permission o f the authors.4PARTICLE PHYSICSExperim ent 182Spin correlation param eter A yy in n-p  elastic scattering (W .T .H . van Oers, D. Ramsay, Manitoba)The purpose o f this experiment was to measure the spin correlation parameter A yy and the analysing power A y in n-p elastic scattering to an accuracy of ±0.03 at 220, 325 and 425 MeV over the angular range 50° to 150° in the centre-of-mass system. The measure­ment was carried out by scattering polarized neutrons from polarized protons in a frozen spin target (FST) and determining the asymmetry in yields with different n-p spin correlations.Polarized neutrons produced at the LD2 target in BL4A by transverse polarization transfer from polar­ized protons were collimated through the 9° port, and the spin direction was rotated to the vertical plane by two spin precession dipoles (Bonnie and Clyde). The recoil protons were detected in the proton range coun­ters consisting of time-of-flight start and stop counters and four delay line chambers. The scattered neutrons in coincidence were detected in 105 cm x 105 cm scin­tillator arrays. The details of the experimental set-up can be found in the University o f Manitoba Interme­diate Energy Progress Report 1987, 1988. The frozen spin target consisted of butanol beads contained in a 5 cm high, 3.5 cm wide and 2 cm thick rectangular box.In order to select n-p elastic events from n-np back­ground four kinematic constraints are formed, viz.:(1) Energy sum: Tp +  Tn(2) Transverse momentum sum:Pp sin 9p cos <f>p +  Pn sin 9n cos cj>n(3) Opening angle: 9P +  6n(4) Coplanarity: <t>p +  <j>nIn calculating the opening angle the deflection of pro­tons in the FST magnetic holding field is taken into account.The maximum target polarization obtained during the run was 84% with a maximum decay time o f 600 h. The target polarization as measured by an NMR sys­tem is known to no better than 4%; however, the present experiment required that it should be known to an absolute accuracy o f 2% . Independent calibrations o f the NMR system using unpolarized protons at the beginning and end o f each data-taking run were done. An unpolarized beam o f 500 MeV protons impinged on a LH2 target or a stack of graphite and produced protons by elastic scattering. The protons scattered at 9° passed through the neutron collimator and a su­perconducting solenoid (Superman), which rotated the unwanted polarization of the secondary beam by 90°. The protons scattered from the FST were detected inproton range counters set at 24° . The recoil protons were detected in the central region o f the big scintilla­tor arrays set at 61°. The p-p analysing power is very precisely known and taken from the phase-shift analy­sis predictions. Thus by measuring the asymmetry and knowing the analysing power the target polarization was measured to the required accuracy.The preliminary data for Ayy and A y at three ener­gies are plotted in Figs. 1-3. The predicted values from different phase-shift analyses and nucleon-nucleon po­tentials are also shown.Experiment 249Radiative muon capture with the T P C(G . Azuelos, TRIUM F; M .D. Hasinoff, UBC)Radiative muon capture (RM C), Z —* isa weak semileptonic process which is particularly sen­sitive to the induced pseudoscalar coupling constant gp of the weak hadronic current. The aim o f this experi­ment was to measure the branching ratio for RMC onAng le  (c .m .)Ang le  ( c . m fFig. 1. (a) Ayy at 220 MeV, (b) A y at 220 MeV.5Ang le  (c .m .)A ng le  (c  m .)Fig. 2. (a) Ayv at 325 M eV, ( b )  A y a t  325 MeV.several light nuclei ( 12C, 160  , 40Ca) in order to deter­mine gp in these nuclei and to look for evidence o f any renormalization away from the expected value for the nucleon (gp =  6.8<7a)- A second purpose of the exper­iment was to investigate the various backgrounds and systematic errors that could contribute to the upcom­ing measurement o f RMC on hydrogen (Expt. 452). The experimental technique has been described previ­ously (1986 Annual Report, p. 8). Preliminary results were presented at the IV Int. Conference on Mesons and Light Nuclei in Czechoslovakia in September [Hasi- noff et al., to appear in Czech. J. Phys.]. The data analysis has been completed and the results discussed below are being readied for publication. Further details can be found in the Ph.D thesis o f David Armstrong [UBC, 1988].Data were obtained for 40Ca using two different Pb photon converters, one o f 1.0 mm thickness and one 0.6 mm thick. The results from the two different data sets were in excellent agreement with each other. Fig­ure 4 shows the data taken with the 1.0 mm con­verter, compared with theoretical predictions for dif­ferent values o f gp. In Fig. 4(a) the theoretical curvesA n g le  (c .m .)Fig. 3. (a) Ayy at 425 M eV, (b) Ay at 425 MeV.are from a phenomenological calculation o f the nuclear response [Christillin, Nucl. Phys. A362, 391 (1981)] and in Fig. 4(b) the theory is a recent microscopic cal­culation [Gmitro et al., Nucl. Phys. A453, 685 (1986)].In both cases the theoretical spectra have been convo­luted with the detector response function. The results obtained with the 0.6 mm converter are very similar. Interpolating the theoretical predictions yields the re­sult gp — (5.7 ±  0.8)pa using the calculation o f Chris­tillin and the similar result gp =  (4.6 ±  1.8)<7a with the calculation o f Gmitro et al. . These results are in good agreement with several previous measurements of RMC on 40Ca [Hart et al., Phys. Rev. Lett. 39, 399 (1977); Frischknecht et al., Phys. Rev. C 32, 1506(1985); Dobeli et al., Phys. Rev. C 37, 1633 (1988)], and indicate a slight downward renormalization o f gp in 40Ca.For 160  two previous measurements o f RMC exist, but they are not in agreement. One group obtained a partial branching ratio for photons o f greater than 57 MeV (relative to the total muon capture rate) of (2 .4 ±0 .5 )x  10-5  [Dobeli et a l, op. cit.,] using Nal(Tl) detectors while the other measurement used a con-6Photon Energy (MeV)Fig. 4. RMC photon energy spectrum from 40Ca, compared to the calculations of a) Christillin and b) Gmitro et al. for different gp. The theoretical curves have been convoluted by the detector response function.ventional pair spectrometer and obtained the partial branching ratio (3.8 ± 0 .4 )  x 10~5 [Frischknecht et al., Phys. Rev. C 38, 1996 (1988)]. The branching ratio de­termined in the present experiment is (2.2± 0.2)x  10-5 , in good agreement with, but more precise than, the former result, but in strong disagreement with the lat­ter result. For 160 ,  only the 1.0 mm Pb converter was used. The present data are compared with the predic­tions o f a microscopic calculation o f the nuclear re­sponse [Gmitro et al., op. cit.] in Fig. 5(a) and with a phenomenological calculation [Christillin and Gmitro, Phys. Lett. 150B, 50 (1985)] in Fig. 5(b). Unlike the 40Ca case, the two models give very different predic­tions for the RMC branching ratio as a function of gp. Using the calculation of Gmitro et al., a value of gp =  (13.6 1 \'t)ga is extracted, indicating a strongPhoton Energy (MeV)Fig. 5. RMC photon energy spectrum from 160 , compared to the calculations of a) Gmitro et al. and b) Christillin and Gmitro for different values of gp. The theoretical curves have been convoluted by the detector response function.upward renormalization o f gp in 160 ; in contrast, us­ing the calculation o f Christillin and Gmitro the value gp =  (7.3±0.9)sra is obtained, in good agreement with the expected nucleonic value gp =  6.8ga. Clearly, more theoretical work is needed before the question o f the magnitude o f the pseudoscalar coupling in 160  can be resolved.Only one previous measurement exists for RMC on 12C [Dobeli et al., op. cit.], in which a partial branching ratio o f (2.7 ±  1.8) x 10-5 , based on a data set o f only 75 events. In the present work, a much larger data set was obtained, with over 600 events af­ter background subtraction, divided equally between the two different converter thicknesses. The data ob­tained with the two different converters are in good mutual agreement and yield a partial branching ratio7M a g n e t icS h ie ld in g(a)Sam pleP h oto  TubeY///////////A \ \ \ \ \ \ \ \ \ ^  ~Ge D etectorCS>Copper S h ie ld ^  |<^Tungsten Shield-^] S c in tilla to r(b)Fig. 6. (a) Schematic diagram of the vacuum system and muonium production target showing the catcher foil inser­tion system, (b) Half of the LLC apparatus showing a beta scintillator and Ge detector.o f (2.3 ± 0 .2 )  x 10-5 , much more precise than the pre­vious measurement. Unfortunately, there is no calcu­lation o f the nuclear response specific to the 12C case available at present. However, if one extrapolates from higher-Z nuclei using a Fermi-Gas model calculation o f the nuclear response [Christillin et al., Nucl. Phys. A 345 , 331 (1980)] the present branching ratio is con­sistent with the expected nucleonic value o f gp =  6.8ga­it is expected that calculations of the nuclear response for RMC on 12C will be available in the near future.Experim ent 304M uonium -antim uonium  conversion (A. Olin, TRIUMF/Victoria)This experiment is a search for conversion of muo-(hh Mu) into antimuonium (/z e+ or Mu ),a reaction which is allowed in some extensions of the standard model. In particular, observable rates for this process are predicted in left-right symmetric models in­corporating an additional Higgs triplet which does not conserve lepton number. Mu mixes with Mu through the exchange o f the doubly charged member of this triplet, while neutrino masses are generated by the neu­tral partner. In terms o f a four fermion effective inter­action with strength G [Feinberg and Weinberg, Phys. Rev. 123, 1439 (1961)] the branching ratio relative to normal muon decay is p xs C  • (G / G f )2 where G f  is the Fermi weak coupling constant, and C  — 2.5 x 10~5. Several previous experiments have searched for conver­sion with the most recent limit [Huber et al., Phys. Rev. Lett. 61, 2189 (1988)] being G  <  0.88G f  (90% confidence) based on the data from our November 1987 data which consisted o f 100 h of exposure. A fur­ther 515 h o f exposure have been obtained and the data-taking for this experiment is now completed. The present experiment probes for the first time interac­tions below the Fermi coupling strength.Positive muons are stopped in the silica powder tar­get (Fig. 6(a)) where they form thermal muonium which diffuses into vacuum with a yield Y  — 2% per incident /i+ . In a large field-free vacuum region, Mu will convert to Mu with probability C ■ (G / G f ) 2- In the vacuum drift space adjacent to the silica, however, conversion must occur before the Mu atom strikes an oxidized tungsten surface on which the /1~ can be cap­tured to form a radioisotope o f Ta. Approximately 19% of the Mu atoms reach the W O 3 surface.Here the /z-  will undergo atomic capture and nuclear capture on W  producing ls4Ta ions. The surface layer is chemically removed after each 12 h /t+ exposure and counted in a shielded low level counting (LLC) appa­ratus at a separate location. Preliminary analysis indi­cates an efficiency o f 3% for these processes (Fig. 6(b)).The 184Ta nuclei (8.7 h half-life) decay by /? emis­sion to excited states o f 184W . A dominant mode in­cludes a prompt 414 keV gamma decaying to an 8.7 /is metastable state. The LLC apparatus detects both radiations together with a delayed gamma from the metastable state. A peak in the delayed gamma spec­trum at 690 keV produced by fast neutrons on Ge was eliminated to reduce the backgrounds. The LLC detec­tion efficiency for the (3-,y--fdei decay sequence is 1.1%. Figure 7 shows the spectra obtained from /z~ irradia­tion of a W  foil showing the effect o f these coincidence requirements.The number N  o f detected antimuonium events is then given byN  =  Np+ ■ C  ■ (G/Gf Y  - Y e (1)where Np+ =  2.0 x 1012 during 515 h o f exposure to /i+ /  The yield Y  was measured with a procedure de­scribed elsewhere, e, the product of the preceding ef­ficiencies and radioactive decay corrections, is deter­mined from /<“  exposures and Monte Carlo calcula­tions.The combined LLC spectra from all /z+ exposures are shown in Fig. 8. No events within 4 keV o f 414 keV are observed in the coincidence histogram. From a pre­liminary analysis of the factors included in e (Eq. (1) implies a limit on the coupling constant o f G <  0.3G f  (90% confidence). The corresponding upper limit on the branching ratio is 2 x 10- 6 . This data will form the basis of T.M . Huber’s Ph.D. thesis. The system­atic study of muonium yield data obtained from this experiment will be the subject of C.A. Janissen’s M.Sc. thesis.Fig. 7. Gamma energy spectra o f the surface layer from a W  foil exposed to /t : (a) all events, (b) events in prompt coincidence with a count in a beta scintillator and followed by a delayed gamma.E n e r g y  (k e V )3 5 0  - 4 0 0  4 5 0  5 0 0  5 5 0E n e r g y  ( k e V )Fig. 8. Gamma energy spectra from all p + exposures (antimuonium runs): (a) all events, (b ) events satisfying the 184 W  coincidence requirements.Experim ent 369Test o f charge sym m etry in n-p elastic scattering at 350 M e V(W.T.H. van Oers, Manitoba; L.G. Greeniaus, TRIUMF)An experiment similar in most respects to the re­cently completed Expt. 121 [Abegg et a l, Phys. Rev. D (in press ); Phys. Rev. Lett. 56, 2571 (1986)] is be­ing prepared for data-taking in the summer of 1989. As originally described the experiment will measure the difference in analysing powers A n and Ap (where the subscript denotes the polarized nucleon) at the zero- crossing angle in neutron-proton elastic scattering at 350 MeV. Designed as a null measurement, the exper­iment is to achieve an accuracy in A A  =  A „-A p of ±0.0008 (or ±0.026° in the zero-crossing angle).The validity o f charge symmetry has been of funda­mental interest ever since it was postulated soon af­ter the discovery o f the neutron. Much circumstantial evidence has accumulated over the years favouring the breaking o f charge symmetry on the order o f a per cent. Although low-energy nucleon-nucleon scattering stud­ies have shown a slight inequality o f the nn and pp scat­tering lengths [Dumbrais et al., Nucl. Phys. B216, 277(1983)], it has proved very difficult to remove experi­mental and theoretical uncertainties to isolate chargesymmetry breaking (CSB) interactions unequivocally.Charge symmetry leads to the complete separation o f the isoscalar and isovector components o f the n-p interaction. This in turn leads to the equality o f the differential cross sections for polarized neutrons scat­tering from unpolarized protons and vice versa. As a re­sult A n(9) =  Ap(9) (the subscripts identifying the po­larized particle). A nonvanishing asymmetry difference is directly proportional to the isospin singlet-triplet mixing amplitude and therefore direct evidence of a charge symmetry breaking term in the interaction.The measurement o f A A  at the zero-crossing an­gle at an incident neutron energy o f 477 MeV has yielded A  A =  (47±22±8) X  10-4 . This result should be compared to the range o f values from the most re­cent theoretical calculations o f (22—7 4 )x l0 -4  [Miller et al., Phys. Rev. Lett. 56, 2567 (1986); Williams et al., Phys. Rev. C 34, 756 (1987); Ge and Svenne, Phys. Rev. C 33, 417 (1986) and erratum Phys. Rev C 34, 756 (1987); Iqbal et al., Phys. Rev. C 36, 2442 (1987); Holzenkamp et al., Phys. Lett. B195, 121 (1987); Brauer et al., Phys. Rev. C 34, 1779 (1986)]. These calculations include (collectively) estimates of contributions from direct electromagnetic effects, the neutron-proton mass difference in one-pion and p ex­changes, and the isospin mixing p°-ui meson exchange.9Fig. 9. Schematic diagram o f the neutron and proton detector arms o f the experimental detection apparatus.Some other smaller effects have also been evaluated. Although the various predictions are similar in magni­tude, they differ significantly in their detailed predic­tions.The 350 MeV measurement will be performed in the manner o f the recently completed Expt. 121. Rather than measuring the asymmetry difference directly, the angles at which the asymmetry crosses through zero will be determined. This difference between the zero- crossing angles is directly proportional to the difference in analysing powers at that angle. Using this technique a null measurement will be performed where the ma­jority o f possible systematic errors cancel because the A n and Ap measurements are made with exactly the same physical apparatus. The only changes are to the polarizations of the beam and target.The 350 MeV neutron beam will be produced in the conventional manner using a liquid deuterium target. A stable proton beam o f intensity ss2 pA  with a po­larization on the order o f 0.80 is required. The time- average current should be at least 1.5 //A . The energy, polarization and position o f the primary beam will be monitored and controlled as in Expt. 121. The proton beam polarimeter/energy monitor has been modified to operate at the higher currents and lower energy. The n-p elastic scattering detection apparatus (shown in Fig. 9) consists o f large solid angle telescopes to detect the neutrons and protons in coincidence. Neu­trons are detected at 33.0° in large area scintillation counters and the recoil protons are observed in scintil­lation counter-wire chamber telescopes nominally cen­tred at 53.0°. The detection apparatus will have reflec­tion symmetry about the neutron beam axis to increase the event rate and allow certain systematic errors to be cancelled. The measurement made with this apparatus allows all systematic errors, except those due to back­ground corrections, to be eliminated to second order at the zero-crossing angle. The solid angle for this exper­iment will be considerably larger than for Expt. 121. This will allow choosing an angle region that is asym­metric about the zero-crossing angle. This in turn will allow attempting a measurement where the interest­ing p°-ui term is relatively large. But note that only the shape o f the angular distribution o f A  A  is acces­sible in these experiments. The analysis o f Expt. 121 data has permitted extraction of the charge symmetry breaking A A  as a function o f angle with some assump­tions about the ratio o f the beam and target polariza­tions. However, the errors are relatively large (±0.0035 for 1.5° lab bins). It will be possible to improve these errors by at least a factor two in the new experiment.Experim ent 400T he Lam b shift and hyperfine structure in muonic atom s (E.E. Habib, Windsor)The purpose o f this experiment is to measure the Lamb shift in light muonic ions. Muons o f momentum 30 M eV /c will be injected into a magnetic bottle con­taining 4He gas. They will pass through a degrader10z  0.0101 1 ' . . . . . . . . . . . . . . . . . . . . . ■ ■ i ' i 1 i 1 i ■0h*0 0.020 OEGOftDEO HU0Ntt v \0 0.000 A \5 I if A j ]  \  /< t  V  ( f i x  / sUJ - 0.020v  11  V _ vmj \ N . /  y y '<  - 0.010r i  rrrnnw p _ - - - - ^ > ' ' ' l N C I 0ENr BENI .~  - 0.060 LLLLIHUN lnMUWllr ^ - - - - - 1u DE6M E PX•“  -n.nfln i , i , i , i , 1 , 1 . 1 . 1 .- 0.100 - 0.000 -0.060 - 0.010 - 0.020 0.000 0.020 0.010 0.060 0.080D IS T A N C E  ( m )Fig. 10. The path o f muons in the magnetic bottle.and the emerging muons o f energy 0-0.6 MeV will be trapped in the magnetic field. After losing energy by collisions with gas molecules, they will be captured to form (muonic-4He) ions.A suitable magnetic field was modelled using two air-core coils and the paths o f muons o f energy 0 to 0.6 MeV were calculated. These calculations showed that the muons stopped within a small region. Since suitable coils were not available, an iron magnet was modified to produce the desired field in the central re­gion. For proper functioning o f the bottle, the muon beam must enter the chamber in a plane perpendicular to the axis o f symmetry and strike a degrader placed 5 cm from the centre o f the field, in a direction within a certain angular range.The first test was carried out using the M13 line with the newly installed separator. The objectives of the first run were: (1) to operate the M13 line and mea­sure the muon flux available; (2) to bring the beam to the desired position in the magnetic field; and (3) to measure the background noise due to 50 MeV elec­trons.The tests were carried out in air without a chamber in the magnetic field. Results were: (1) the background noise due to electrons is not a problem, due to the effectiveness o f the separator; (2) the muon flux was smaller than expected but still usable.Figure 10 shows the path of the muon beam in the magnetic field and the path o f a degraded muon. The emerging beam, after the degrader, consists o f elec­trons. The paths are in the central plane. The mea­sured field values were used in this calculation.Experim ent 452Radiative muon capture (R M C ) on hydrogen(G . Azuelos, TRIUMF; M. Hasinoff, UBCRadiative muon capture (RM C) on hydrogen (p _ +  p —* n +  v +  7 ) is the ultimate goal o f all muon capture experiments. The high sensitivity o f the rate o f RMC to gp, the induced pseudoscalar coupling constant in the weak hadronic current, stems from the fact that, at high photon energies where q2 —* m2 , the pion prop­agator (q2 — m \)~l becomes very large. Furthermore, RMC from the singlet state o f the pp atom or, equiva­lently, (in liquid hydrogen) from the ortho state o f the PUP molecule, can be represented as a two-step process where the photon is first emitted, thereby leaving the pp system in a triplet state. Ordinary p capture then follows. It is well known that p capture from the triplet state is nearly 15 times more sensitive to gp than cap­ture from the singlet state. The major difficulty o f the experiment, however, lies in the very low rate expected for this process: about 6 x 10-8  o f the stopping p ’s will undergo RMC.The average o f five measurements o f gp on the proton [Bardin et al., Nucl. Phys. A352, 365 (1981)], obtained from ordinary p capture on hydrogen has a precision of 22% (gp =  8.7±1.9), although each o f the experiments contributing to the average has an error in excess of 40%. Radiative p capture on hydrogen has never been measured before. In the present experiment we expect to achieve a 10% precision. The systematic error will be dominated by the uncertainty in the ortho —+ para transition rate in liquid hydrogen and by the tails of the response function o f the detector.A series o f measurements o f the RMC rate on light nuclei has now been completed (see Expt. 249), using the TRIUMF time projection chamber (TPC ) as a pair spectrometer. We have taken advantage o f the experi­ence gained in these measurements to design the detec­tor system for the present experiment. In the last year our major effort has been directed in the construction o f the various components.A new drift chamber, based on the design o f the BNL787 chamber, has been built (Fig. 11) to replace the TPC. It is enclosed by an inner and an outer car­bon fibre cylinder and consists o f four layers o f drift cells, the third one having the wires strung with a stereo angle o f 7.5o. Each cell is about 5 cm long with a drift distance o f 2 cm. It has 10 anode wires, the inner six o f which are sense wires o f 20 pm diameter Au- plated W . The drift field is provided by 19 Au-plated Al wires placed on each side o f the anodes. Each wire is crimped in a pin inserted in a feedthrough hole which defines its position. Careful measurements o f the vari­ations o f the hole position in the anode and cathode1112Fig. 11. Side view dc installation in Chicago magnet.t I \'  1 IFig. 12. Cosmic-ray track in the drift chamber.feedthroughs showed that initial tolerances were well met (about 50 pm ). While stringing the nearly 8000 wires, measurements o f their tensions were done regu­larly to monitor the stresses on the end plates. String­ing was completed in September and initial tests with cosmic rays have already begun (Fig. 12). The pream­plifiers and postamplifiers as well as the cabling for the readout o f the chamber signals have all been built and tested.Modifications to the Chicago magnet have been made to accommodate a new set of trigger scintillators installed around the chamber. In particular, a number of holes (40) were drilled in the front end plate for the scintillator light guides. New field mapping measure­ments were made and these were found to be in good agreement with calculations. The trigger scintillators and converter are now mounted (Fig. 11), as well as the new beam counter package.Other major components o f the detector are: (1) The Asterix cylindrical wire chamber and associated elec­tronics which have been shipped from CERN; every­thing has been tested and is now ready to be mounted in the magnet. Together with the stereo layer of the drift chamber, this cylindrical chamber will serve to define the angle o f the track with respect to the beam direction. (2) The cosmic-ray veto drift chambers and scintillators which were used in the TPC run; they have been completely recommissioned with new wires and preamplifiers. They are now mounted above the magnet. (3) The electronics setup for the trigger andP h o to n  E n e rg y  (M e V )Fig. 13. Monte Carlo spectrum.data acquisition has been set up using ECL logic and FASTBUS T D C ’s in a completely reorganized counting room.Construction efforts were also applied in other essen­tial subsystems: (1) The M9 beam line has been rebuilt with one leg going to the superconducting muon chan­nel, and the other to the Chicago magnet. Initial beam tuning has been done. The rf separator is getting a major refurbishing for use in this experiment. (2) The target design, based on extensive Monte Carlo calcu­lations, has been completed. The flask will be made of 250 pm  Au surrounded by Ag heat shields. Dummy targets made o f Cu have been built for testing. The construction o f the liquid hydrogen refrigeration and purification systems is presently in the hands o f the cryogenics group.Finally, considerable progress has been made in all aspects of the software: data acquisition, analysis and Monte Carlo. Extensive Monte Carlo calculations have been performed on all available computers, including TRIUMF and Univ. de Montreal ACP systems to eval­uate the backgrounds from radiative muon decay and from decay-electron bremsstrahlung (Fig. 13).Initial RMC rate measurements will be made in the spring o f 1989 with nuclear targets. It is expected that the first runs on a liquid hydrogen target will take place in the autumn.Experim ent 497M easurem ent o f the flavour-conserving hadronic weak interaction (J. Birchall, 5.A . Page, W.T.H. van Oers, Manitoba; G. Roy, Alberta)The collaboration is currently in its first year o f a two-year instrumentation development and engineer­ing program in preparation for a measurement of par­ity violation in p-p scattering at 222 MeV. This ex-13periment is based on a modified version o f our ear­lier proposal, which has been described in previous TRIUMF Annual Reports (Expt. 287). Experiment 497 will determine the parity-violating longitudinal analysing power A z in p-p elastic scattering at 222 MeV to a precision of 2 x 10-8  in two independent geometries simultaneously, which will provide a crucial consistency check on the results. The beam energy has been chosen to ensure that only the D-i) partial wave con­tributes to A z , as confirmed by recent Monte Carlo calculations for the proposed apparatus. This is in con­trast to the situation at low energy (T  <  50 MeV) where the (15o-3Ro) partial wave gives rise to the measured parity-violating asymmetries [Kistryn et al., Phys. Rev. Lett. 58, 1616 (1987)]. In the conventional weak meson exchange model o f the parity-violating N- N  interaction, the partial wave amplitude isdue entirely to weak p exchange, and thus a measure­ment o f A z at 222 MeV enables the weak p-nucleon coupling constant to be determined.The true parity-violating asymmetry depends only on the helicity o f the incident proton beam. False asym­metries may arise from helicity-correlated changes in other beam properties such as position, direction, in­tensity, transverse polarization, or energy, which must be reduced to an absolute minimum during the experi­ment. The approach taken is to eliminate or drastically reduce modulations o f all beam properties other than helicity and to minimize the sensitivity o f the detec­tion apparatus to changes in beam properties. We are working closely with the TRIUMF ion source group to optimize the performance o f the new laser pumped polarized ion source, which is crucial to the successful outcome o f the experiment.To reduce false asymmetries due to beam-intensity modulations, the ionization chambers used to mea­sure the beam intensity upstream and downstream o f the liquid hydrogen target must be highly linear (fig/d <  10-5 ). Engineering runs have determined that in order to give the required linear operation at the 500 nA beam current that is planned for the experi­ment, the ionization chambers must be operated at re­duced pressure and high voltage to ensure total charge collection in dc mode. The dependence of beam inten­sity upon spin state has been measured for the optically pumped polarized ion source (14), using prototype in­beam ionization chambers, as shown in Fig. 14 (30 nA, 290 MeV). The intensity is seen to drop by 3% between the polarized and unpolarized states, but the variation o f beam intensity upon spin reversal is found to be less than 0.1% (6 ± 2 x l0 -4  in this figure). These re­sults are extremely encouraging, since the source was not yet fully optimized during the tests, the degree of polarization during this run being only 30%. Work isFig. 14. Beam current as a function o f time following spin flip. (Laser pumped polarized ion source: I =  30 nA, P ~0.3; averaging time: ~15 min.)continuing at TRIUMF on improving both the polar­ization and intensity o f the optically pumped polarized ion source.To reduce false asymmetries due to the relatively large parity-allowed analysing power A y (~ 10 -1 ), small transverse polarization components which may be present in the longitudinally polarized beam must be minimized. It is necessary to measure the profile o f residual transverse polarization components within the beam envelope in order to compensate for such ef­fects in the final data. Initial measurements have been made, using the target deployment system (TDS) at the T1 target location on beam line 4B. A series of strip targets were mounted on the target ladder, which was scanned slowly through the beam while horizon­tal and vertical scattering asymmetries were measured. Preliminary results for a polarization scan are shown in Fig. 15. Measurements were made with the Lamb shift polarized ion source, as the optically pumped source was not sufficiently stable at the time o f the run. A po­larization monitor based on a carbon blade which scans through the proton beam, synchronously with 4 inte­grating ion chambers, has been designed to meet the precision requirements o f the parity-violation measure­ments, as indicated by systematic error calculations. This detector will be built and tested in the coming year at TRIUMF.Systematic errror estimates based on a net trans­verse polarization o f 0.001 have shown that the beam centroid must be stabilized at two points on the sym­metry axis of the apparatus to a few pm. Our pro­totype single loop feedback system, described in ear­lier Annual Reports, successfully reduced beam excur­sions to this level at frequencies up to 1 kHz. Four new 20 A, 55 V power supplies have been designed and140 . 4 -3  -4  — -5  - | -------------------- 1---------------------1-------------------- 1-------------------- 1---------------------1-------------------- 12 1 3 0  2 1 4 0  2 1 5 0  2 1 6 0  2 1 7 0  2 1 8 0  2 1 3 0  2 2 0 0T R R G E T  P O S I T I O N  Fig. 15. Preliminary results for polarization scan of longi­tudinally polarized proton beam on beam line 4B. The plot shows the helicity-correlated Px as a function o f y position. The horizontal scale is in units o f 0.01 in. (beam diameter ~  1.5 cm ).custom built at the University o f Alberta for the feed­back system, and new analog dividers designed and built at TRIUMF have been installed and tested. In August a two-loop system was operated and tested at 500 nA. It required no further gain or offset ad­justments unless the beam was catastrophically inter­rupted and restored to a position beyond the steering range o f the aircore magnets. Although the prototype feedback system based on split-plate ionization cham­bers has been extremely successful at controlling beam position excursions, the relatively thick windows and sense planes o f these detectors cause a large amount o f beam broadening which cannot be tolerated for the parity-violation measurements. A dual function beam intensity profile monitor, which will greatly reduce the amount o f material in the beam path, has just been completed and preliminary testing is under way at TRIUMF. The monitor contains split foils to provide input signals to the beam position feedback loop which will stabilize the median o f the beam-intensity distribu­tion in x and y to ± 3  ym . The monitor also contains harps of 12 ym  gold-plated tungsten wires at 1 mm spacing for measuring the beam intensity profile.Once the key beam diagnostic elements have been completed and independently calibrated, we will focus on a programme o f test measurements to determine the sensitivity o f the apparatus to moments o f trans­verse polarization as well as beam intensity and posi­tion modulations. The results o f these tests will be cru­cial in determining the next stage o f the experiment.Study o f rare K  decaysB N L  787 (B N L -P rin c e to n -T R IU M F  collaboration)(D. Bryman, TRIUMF/Victoria)Unique opportunities to test the standard model are offered in the study o f K  —► tyvV because reliable higher-order calculations assuming three generations can be confronted by experiment.Bounds on the rate for K + —+ ■k+ vv have been in­ferred from K°l —> y y , from semileptonic B-meson de­cays, from the measured 6-quark lifetime and from the large observed B^-Bj] mixing. The predicted branching ratio lies in the region 1 to 7 x lO -10 depending on the top quark mass and mixing angles. Conversely, a mea­surement o f the branching ratio would be significant in constraining these parameters and would allow a direct test of higher-order weak corrections in the standard model.A well-specified standard model expectation for the K + —► v + i'V branching ratio is the foundation sup­porting the use o f the reaction to search for new physics in the form o f extra generations or new types o f parti­cles or interactions.In addition to searching for reactions like K + —+ ir+ i'V, BNL Expt. 787 is also studying a number of other rare kaon decays including K + —► t + y +y~  andK +  „-+yy.The 787 detctor has a large geometrical acceptance (27r sr) for the K + —► ir+vv decay mode, while aim­ing to maximize the rejection o f background processes such as K T2, K)i2 , K + —> y + v y  and others. Sensi­tivity for identification o f unaccompanied pions from K + —» 7r+ vV is accomplished through measurements o f momentum, kinetic energy, range, decay sequence 7r —*■//—+ e, and nearly 47r coverage for detection of photons.The detector assembly was completed in March, and the first experimental run followed immediately and continued through May. After initial shakedown o f the apparatus every subsystem o f the detector was found to perform well and met expectations.Figure 16(a) shows an example of a calibration event o f the type K + —► 7r+ 7r°. A blow-up o f the segmented target is shown in Fig. 16(b). Energy and time for each target element are available at present from an ADC and a TD C, respectively, so that incident kaon and outgoing pion elements can be identified. The momen­tum calculated from the track in the drift chamber is 198 MeV, determined with resolution ap =  2.5%. The pion track energy is found by summing the range stack and target energies to be 97 MeV with a resolution of <7e ~  3% and the range is 31 g /cm 2 with a resolution o f ctr & 3%. Correlation o f range energy and momen­tum are used to verify that the particle is a pion. In15a)C22D( 3Fig. 16. (a) K W2 event, (b) Target blowup, (c) r-(i in stopping counter.16addition, the 7r —► fiv decay pulse is observed using the transient digitizer in the last range stack counter hit, as shown in Fig. 16(c). The energy and timing of the 4 MeV muon pulse can be obtained and checked for consistency o f position using the two ends of the counter. The /i —* evv  decay is also observed with the TD during an inspection period of 5 /is. In this event the two photons from ir° —* 77 are both observed. We have determined from data that the inefficiency o f the photon veto system is eno <  4 x 10~6 for 7r°’s from I<w2, which is consistent with expectations o f the Monte Carlo calculations.The central drift chamber system was entirely de­veloped at TRIUMF. The active volume is enclosed by Al endplates and graphite-epoxy cylindrical walls. The chamber is arranged in five layers o f multiple sense-wire cells. Three layers are axial and two are at a stereo an­gle o f 3.5°. The wires are staggered by 500 /im from the cell axis to provide local resolution o f the left-right ambiguity. Six central sense wires are used resulting in up to 30 points measured on a track. The Lorentz angle o f drift is 25° for a magnetic field o f 1 T. Since only the central six wires are used, there is no loss of efficiency and a good distance vs. time relationship is maintained throughout.The electronics built at TRIUMF consists o f an on­board low power (30 m W ) hybrid preamplifier with output transmitted to an amplifier-discriminator. Drift times are measured with LRS 1879, 500 MHz Pipeline TDCs. The measured rms resolution from the elec­tronics system is approximately <rt ~  1 ns, result­ing in a 50 i^m uncertainty for argon-ethane gas with Vd =  5 cm//xs. The typical minimum position res­olution obtained under operating conditions is cr ~  150 nm, which results in momentum resolution o f ap­proximately 2.5%.The TRIUMF group also constructed the two lead- scintillator sampling calorimeter endcap veto detec­tors. Together these detectors cover 37% o f the solid angle. NE104 scintillator and lead sheets are positioned transverse to the beam axis and 24 azimuthal segments are read out via BBOT wave length shifter bars by phototubes located outside the magnet. The detector produces 10 photoelectrons per visible MeV energy de­posited, which allowed a low threshold of 1 MeV to be used.The energy calibration and the balance of the end- caps was done using monoenergetic muons from the de­cay K + —► The technique is also used to monitorany changes in the gains o f the phototubes. By mea­suring the energy o f the two photons coming from the decay o f the monoenergetic 7r°’s o f the K + —> 7r+ 7r° de­cay and thus reconstructing the energy, the fraction o f visible energy over incident energy was determinedto be 0.312, consistent with expectation.The beam counter system consists o f several scin­tillators, two scintillator hodoscopes, three planes of MW PCs and a Cerenkov counter. All but the latter were built at TRIUMF. The M W PCs use a fast CF4 gas mixture and special home-built hybrid electronics including the post-amp/discriminator system built for the central drift chamber. All elements performed well at the highest rates (up to 5 MHz) encountered. A new hodoscope and several new beam veto counters are be­ing constructed for the 1989 run.Two types of 500 MHz transient recorders (TD ) will be used in Expt. 787. 100 channels o f TDs built at BNL using a Tektronix FADC were operational on the range stack during the 1988 run. Another 100 channels are anticipated for 1989. A prototype TD  system based on the TRIUMF 128-bucket gallium arsenide CCD is un­der development at TRIUMF with the goal o f installa­tion during 1989. The 500 MHz CCDs offer potentially a wide dynamic range (> 9  bits) TD at low cost (total cost <$350/channel is the objective). The readout of the CCDs will be accomplished using 15 MHz FADCs packaged in FASTBUS developed by a Delphi group at Ames, Iowa. 64 channels of the Ames FADC are presently operational at TRIUMF.The data acquisition system for Expt. 787 for the 1988 run consisted o f three main components:• A FASTBUS-based system made o f 7 crates daisy chained to each other via SSP microprocessors that were each recording data independently during the beam spill. Event rejection based on energy sums from the ADC data and ?r-/i recognition from the transient recorder data was implemented in the various SSPs.• A CAMAC-based system used for controlling and monitoring the ADCs and high-voltage supplies.• A group of VAX computers linked via Ethernet. One computer was connected directly to the FASTBUS system, another to the CAM AC system, and the third one was dedicated to monitoring the data.Reconstruction routines for the drift chamber, beam counters, range stack and endcap veto have been writ­ten by members o f the TRIUMF group. A package of subroutines has been written which outputs the results o f the reconstruction so that it is not necessary to redo the reconstruction on subsequent passes through the data. A version of the analysis program KOFIA with all its reconstruction routines has been written for the ACP microprocessor farm computer system as well as for VAXes.Analysis has been performed using the ACP system on all the valid K  —* ni'T' data taken during the 1988 run. Refinements including fitting o f the transient dig­itizer data have been incorporated in subsequent anal­17yses. Work is also proceeding on determining all ac­ceptance and efficiency factors so that a result from this dataset may be obtained. In addition, parallel ef­forts are in progress to analyse K + —* n+ p + p~ and K + —* tt+ 77 data and to determine the magnitude of potential backgrounds for the K + —+ 7r+ m/ search.Potentially good quality data for the K + —+ 7r+ vV experiment were taken during the last few weeks o f the 1988 run at a beam rate o f approximately 150 K K + stops/pulse. These data are presently being analysed and are expected to provide an improved sensitivity over previous searches for I\+ —► n+ uT'.M easurem ent o f A —► ny  B N L  811 (B irm ingham -B N L -B oston-C ase  W estern -N ew  M ex ic o -P rin c eton -T R IU M F -U B C  Collaboration) (D .F . Measday, UBC)The results for the 1987 run have now been com­pletely analysed and most o f the manuscripts have been submitted for publication.The decay E+ —► py was the thesis o f Nigel Hessey of Birmingham University. The observed branching ratio was (1.45±0.20±0.11) x 10~3 with 408 events, which is a significantly larger data sample than previous exper­iments. The result is consistent with other results and the overall error comparable to typical experiments.The other two completed theses are from Boston University and concentrated on the data taken with the high-resolution 7-ray detector BUNI. Negative kaons were stopped in both hydrogen and deuterium targets and the singles 7-ray spectrum was observed. The the­sis of David Whitehouse was on the hydrogen data, and two capture reactions were cleanly observed for the first time. The branching ratios, at rest, areI<~p —> At  BR =  (0.86l°;J3) x 1(T3 (499 events)K ~ p  —► Ey  BR =  (1.44±0.23) x 1(T3 (850 events)The A7 ratio is significantly less than a previous ob­servation but the line was not cleanly identified in that measurement. The Ey  reaction had not been observed before. Both branching ratios are less than predictions o f the cloudy bag model and the nonrelativistic quark model. The phenomenological model o f Fearing and Workman has a little difficulty with the very low value for A7 , but is the most satisfactory o f available calcu­lations.The reaction K ~ d —► Any  at rest was also observed for the first time with the measured branching ratio beingK ~ d  -► Any BR =  (1.94±0.12±0.20) x 1(T3 .It is surprising that it is larger than the branching ratiofor K ~ p  —► Ay. The shape o f the spectrum is consistent with a reasonable An final-state interaction. However, the data are not adequate to obtain an improvement on existing measurements o f the scattering lengths a, and a*.The experiment equipment was completely removed in 1987 and the crystal box from LAMPF was placed in the LESB II channel. During the spring run 1988 data were taken with the crystal box, with a view to observing the rare decay A —► ny. Over 1200 magnetic tapes o f data were accumulated but we shall be lucky if the density o f useful events is more than one per tape. The on-line analysis showed that everything was working reasonably but a lot o f off-line analysis will be required to separate out the signal. This will become the thesis o f Anthony Noble o f UBC.A second run will occur January-March 1989 and there will be less need for engineering checks, so more useful events should be observed. We also intend to have some data with in-flight kaons to find how the detector responds. Unfortunately the main crystals are only 12 radiation lengths deep (30 cm o f Nal), so the resolution for higher-energy gamma rays will be quite poor. One needs about 18 radiation lengths for a few hundred MeV 7-ray if you want 3% to 5% energy res­olution. For comparison the crystal barrel at LEAR is composed of modules 16 radiation lengths deep (30 cm o f Csl). It also has a much larger coverage of solid angle and 1380 crystals, so it is a formidable new detector and defines the present state o f the art. However, we can obtain some useful technical information with the crystal box and will use this for defining detectors for KAON.M easurem ent o f spin-dependent observables in the pp elastic scattering from  450 to 700 M e V /c  C E R N  P S198(D .R . Gill, G.D. Wait, TRIUM F)The theoretical approach to N N  scattering is mainly based on potential models. The first ingredient o f this description is a form o f theoretical N N  potential, based on meson exchange, which is G-parity trans­formed to an N N  potential. This G-parity transforma­tion reverses the signs o f the potential contributions of the odd G-parity meson exchanges. Important in this representation is the tendency for all mesons to yield a contribution o f the same sign to certain components of the interaction. In the N N  system, scalar and vector meson exchange add coherently in the spin orbit term, while they tend to cancel in the central part. In the N N  potentials coherences occur in the central, tensor and quadratic spin orbit contributions. This different behaviour leads to the strong N N  attraction and is ex­pected to have very striking consequences for spin ob­18servables. The second ingredient in N N  models is some kind o f annihilation mechanism. The annihilation cross section is large and is responsible for the large imagi­nary part o f the potential. Several different approaches exist for describing the annihilation, all with results that fit reasonably well the existing data on the spin- integrated cross sections. For the spin-dependent ob­servables the situation is completly different: the pre­dictions depend consistently on the theoretical inputs. Therefore the measurement o f spin observables in the pN elastic scattering will provide useful constraints to define the proper set o f parameters of the N N  poten­tials. This, provided that the data are obtained over the full angular range, because the different theoreti­cal predictions differ significantly in different angular domains.This was the main motivation o f Expt. PS198 per­formed with the antiproton beam of the LEAR facility at CERN. Measurements were made o f the full angu­lar distribution o f the differential cross section dcr/dQ and of the analyzing power A y in pp elastic scatter­ing at 450, 550 and 700 M eV /c. Thus far only the 700 M eV /c data has been submitted to a preliminary analysis. At this energy data on dcr/dQ have already been published [Eisenhandler et al., Nucl. Phys. 113, 1 (1976); Kageyama et al., Phys. Rev. D 35, 2655(1987)]. In regard to Ay a few points, with large error bars, have been measured in a double scattering ex­periment [Kimura et al., Nuovo Cim. A71, 438 (1982)] and, more recently, data in a more restricted angular domain, have been produced at 679 and 783 M eV /c [Kunne et al., Phys. Lett. B206, 557 (1988)].The experimental setup is shown schematically in Fig. 17. Monitoring o f the beam was provided by counter (1). This counter consisted o f a thin scintil­lator F, 0.3 mm thick and o f an antihalo scintillator FH, 5 mm thick, with a circular hole o f 2 cm. FH was put in anticoincidence with F to give the signal F0. When the beam was focused on the polarized target(2),typical counting rates o f FH were less than 2% of F. An additional relative monitoring was provided with counter 3 (Fig. 17), that consisted o f two scintillator slabs put to view the target at 0° but out o f the scat­tering plane and the acceptance of the spectrometer. The polarized target consisted o f a slab o f pentanol 5 mm thick, 1.8 cm high and 1.8 cm wide. The 2.5 T  magnetic field, needed to polarize the protons, was pro­duced by a superconducting split coil magnet supply­ing a vertical field. The proton polarization was deter­mined by comparing the dynamic polarization signal with the natural polarization signal at thermal equi­librium. Typical polarization values o f approximately 0.80 were obtained with relaxation times in the frozen spin mode o f the order o f 150 h. The scattered particleswere detected and momentum analysed with the mag­netic spectrometer SPESII. In order to cover the full angular domain in the c.m. system, we detected p for the forward c.m. angles and the recoil p for backward c.m. angles, rotating and/or reversing the magnetic field o f SPESII to get the convenient c.m. angular set.The detection system o f the spectrometer consisted (Fig. 17) o f four M W PC, all o f them with x  and y planes, and a scintillator counter S. The trigger was F0*S. A precise measurement o f time o f flight, made with these two counters, provided the appropriate se­lection o f the required particle (p or p) against the other products, mainly pions, o f the interaction o f the p beam with the target. With the co-ordinates at the focal plane and the transfer matrix o f SPESII the com­plete kinematics o f reaction was reconstructed, and the missing mass determined. In this way the pp elastic channel was seperated from the contributions of the nuclear content o f the target. Around (?iab ~  45°, where the energy o f the detected particle was minimal, angu­lar and energy straggling considerably deteriorated the resolution on the missing mass. In order to investigate the possible contaminations from quasielastic scatter­ing or other reactions on the nuclear content of the tar­get we added a recoil counter. This was put at 0 ~  90° with respect to SPESII and rotated with it. It con­sisted o f a scintillator slab and a MW PC, with x and y planes and covered the full acceptance o f SPESII. It was efficient for the detection o f the recoil particle, p or p, in the angular domain 70° <  c.m. <  110°. Through track reconstruction and coplanarity selection it was shown that, even in that angular domain, background contamination was negligible.In a preliminary run with a proton beam the ap­paratus was checked by measuring dcr/dQ. and A y in pp elastic scattering. The results were consistent with phase-shift compilations. From the measured p spin- dependent cross sections at 702 M eV /c the prelimi-191■  h *  ' i l l------------------- 1—  —  iPP —  PP1i t  1 ♦- [ M iil.  PS 198 70 0  M eV /c  pre l im inaryi _ l -------------------------------.cos 0 CMFig. 18. The data o f the analysing power A y. The error bars include systematic errors.nary angular distribution o f the pp analysing power A y shown in Fig. 18 has been computed.20NUCLEAR PHYSICS AND CHEM ISTRYExperim ent 300Polarization transfer in the pp —► dw+ reaction(D .A . Hutcheon, TRIUM F)Complete determination o f the amplitudes for pp —► drr+ requires measurement o f “polarization transfer” , that is, the correlation o f proton beam (or target) polarization with the polarization o f the outgoing deuterons. Partial-wave amplitude fits by Bugg and by Watari and collaborators have included other available spin observables involving polarized beams and/or tar­gets. These data left poorly constrained certain phases between amplitudes, with the result that the Bugg and Watari solutions predicted vastly different vector-to- vector polarization transfers in pp —► (Itt+ . This situa­tion led us to make a measurement o f the sideways-to- sideways polarization transfer K ss at 507 MeV using the focal plane polarimeter (FPP) o f the medium res­olution spectrometer at TRIUMF.As reported in last year’s Annual Report, we ob­tained asymmetry data at seven centre-of-mass angles in the range 20° to 155°. In October o f this year we were able to measure the analysing powers for the FPP using a polarized deuteron beam. This was done at the Laboratoire National Saturne synchrotron in a set­up which produced all o f the polarization components i tn , <20, <21, and <22; analysing powers were measured at 150, 200, 275 and” 350 MeV.W ith these results we are able to make a precise prediction for measured asymmetries given a partial- wave amplitude solution. Figure 19 shows our asymme­try data compared to the Bugg and Watari solutions. There is a clear-cut preference for the former solution.D euteron c.m . angleFig. 19. Our results for polarization transfer in the pp —► (<7r+ reaction at 507 MeV. The curves are predictions of partial-wave amplitude sets fitted to previous data.Experim ent 328M ulti-nucleon m odes in pion absorption on 4 He(P . Weber, UBC)For a long time the understanding o f pion absorp­tion in nuclei was dominated by the picture of 27V- absorption nN N  —*■ TV TV (quasifree absorption), in analogy to the free nd —*■ TV TV case. The measurement o f quasifree absorption in carbon 12C(7r+ ,PP) at T\ — 165 and 245 MeV [Altman et al. (Phys. Rev. Lett. 50 1187(1983)] with only 10% 27V-absorption out of the total absorption cross section shed some doubts on the prevalence o f the quasifree absorption model. Recently pion absorption measurements with 3He have been per­formed at TRIUMF and PSI (SIN) also in kinematical regions, where 27V-absorption is strongly suppressed. A three-nucleon absorption cross section proportional to the three-nucleon phase space (constant matrix el­ement) has been reported by Backenstoss et al. [Phys. Rev. Lett. 55 2782 (1985)]. The results by Aniol et al. [Phys. Rev. C 33, 1714 (1986)] reveal proton en­ergy spectra proportional to phase space, whereas the two-fold differential cross sections fluctuate by a fac­tor o f two, depending on the choice o f the counter geometry. The ratio o f 3TV to 27V absorption is sur­prisingly high, although different for the two experi­ments. The 37V absorption cross sections amount to 20-40% o f the total absorption cross section between Tn =  62 and 120 MeV. It is important to investigate this absorption process in further detail as the reac­tion 7r +  37V —► 37V implies an interaction of a pion with three nucleons. In Expt. 328 n+ absorption in 4He has been studied at Tw =  165 MeV. The experimental set-up in the TRIUMF M il  area consisted of a liquid 4He target and four detectors (Fig. 20). Three pro­ton coincidences from the reaction 4He(?r+ ,ppp)n were accepted in any counter combination that allowed a kinematically complete analysis o f this reaction. In two detectors (RA ,R B ) the protons were stopped, whereas the other counters (TA ,TB ) measured time of flight over a distance o f 2 m.All four counters were equipped with wire cham­bers (M W PC), allowing trajectory determination and target traceback. Thin dLT-counters were placed in between the target and each detector, allowing a hardwaxe-trigger on charged particles, and enabling particle separation in dE-E  plots during the software analysis (Fig. 21). The energy response o f RA and RB as well as the time o f flight for TA and TB were cali­brated via the two-body reaction itd —► pp with a liquid deuterium target. The properties o f RA and RB are described in detail by Z. Papandreou et al. [Nucl. In- strum. Methods A268, 179 (1988)]. The time-of-flight21Fig. 20. Typical set-up for Expt. 328.resolution for TA and TB is better than 1 ns and trans­lates to an energy resolution o f 10 MeV (FW HM ) at 100 MeV proton energy. The coincidence measurement o f three protons after pion absorption in 4 He is kine­matically complete.First results are reported here from a geometry with RA at 40°, RB at 100° and TA at -7 0 ° , respectively. During the software analysis cuts were imposed on the proton bands in three detectors (Fig. 21), good wire chamber information was required, and the event had to be originated from the target cell. For the data interpretation a Monte Carlo programme calcu­lated three-nucleon and four-nucleon phase space with built-in geometry and energy thresholds. The analysed events can be compared with the MC simulation inRR t a r g e t  e n e r g y  t i e V *  1 0Fig. 21. dE-E  plot showing the particle separation in RA. The solid curve defines the cut on protons.all energy and angle variables. It is, however, conve­nient to concentrate on a variable, which reveals infor­mation about the reaction mechanism. The momen­tum pn o f the undetected nucleon (spectator) seems to be an appropriate variable to calculate from the ex­periment and MC simulation (Fig. 22) contains the measured neutron momentum distribution, along with the MC simulation o f quasifree three-nucleon absorp­tion. There is substantial agreement between measure­ment and simulation in the momentum region o f 0-  250 M eV /c, indicating that the x + was absorbed by three nucleons having opposite Fermi momentum to the spectator neutron. A  second bump around 300 M eV /c can be attributed to final-state interaction of one o f the outgoing protons with the spectator neutron.The result o f this experiment can be directly com­pared to an experiment at PSI [Backenstoss et al., Phys. Rev. Lett. 61, 923 (1988)], where 120 MeV x+ were absorbed in 4He as well. Three-proton coinci­dences as well as ppn-coincidences were recorded si­multaneously. The analysis in terms o f the spectator momentum distribution leads to the same conclusion. The second bump at 300 M eV /c has been observed even stronger, which can be explained by the special geometry, favouring final-state interaction.E x p e r im e n t  331S p in -tra n s fe r  m e a su re m e n ts  in  w+d  —<• p-\-p( G. Jones, UBC)An extensive program of spin-dependent measure­ments o f the p+p  —► d + x  reaction has been carried out in recent years in order to provide an experimental determination o f the partial-wave amplitudes for thisFig. 22. Neutron momentum distribution for the reaction 4H e (x + ,ppp)n.22fundamental pion reaction. Most o f this work has in­volved the measurement o f spin-correlation parameters obtained by bombarding a polarized proton target with a polarized proton beam. It has been clear, however, that additional measurements which depend on the deuteron spin are required before a unique amplitude determination can be carried out. The first o f these, itn , the vector analysing power, was measured (for the inverse reaction) by utilizing a polarized deuteron tar­get. The remaining measurements which are required are the spin-transfer parameters. Although these have been known to be extremely important in constraining the partial-wave amplitude fits, they have experimen­tally been the most challenging to obtain.Our approach for measuring the spin-transfer pa­rameters also utilizes the inverse reaction. It involves the measurement o f the polarization o f one of the out­going protons when the pion is absorbed on a polarized deuteron target. This year measurements o f K n n  were measured for a proton angle (lab) of about 30° for pion kinetic energies o f 105,140, 180, 205 and 255 MeV (cor­responding to proton energies in the inverse reaction o f 500, 570, 650, 700 and 800 MeV, respectively). This data represents the completion o f our program o f mea­surements o f K l s , K ss and K n n  initiated last year.This technique provides the benefits o f a well-defined deuteron vector polarization (typically >30%, with an additional small, calculable tensor component), to­gether with straightforward “polarimetry” techniques for measuring the polarization o f the outgoing pro­ton. From the tensor information, in fact, Mathie et al. (Regina) will be analysing the data with a view to extracting the tensor analysing power for the reaction (Expt. 303).The production of proton pairs from background re­actions associated with pion absorption in the nuclear target material was distinguished from the reaction of interest by imposing appropriate kinematic constraints on the two-proton events. By imposing appropriate cuts on the polar and azimuthal angular correlations, the background contamination could be reduced to a level o f a few per cent. In order to reduce the amount o f data stored on magnetic tape, a front-end proces­sor (SEN J - l l  Starburst) was employed to reject any events associated with a scattering angle in the carbon o f the polarimeter by less than 6°.The technique was tested by analysing a set o f un­polarized target runs. The data were obtained for pi- ons o f 205 MeV with the polarimeter at an angle of 27° (lab). During these runs a longitudinal magnetic field at the target was maintained at the usual value o f 2.5 T . The normal component o f the polarization o f the outgoing protons is known (by time-reversal in­variance) to be equal to the analysing power for theTable I.Measured Predictedpolarizations polarizations(% ) (% )Normal polarization 36.5±2.4 36.5Sideways polarization 10.8T2.5 12.6inverse reaction: p+p  —► d+ir (a reaction which has been extensively studied in this energy range). Since the deuterons in the target were unpolarized, there is no sideways component o f the polarization o f the out­going protons. For an unpolarized target, then, both components o f the transverse polarization o f the out­going protons are known, a situation ideal for testing the analysis algorithms, especially susceptibility to sys­tematic errors. By maintaining the magnetic field at the same value as that required for the spin-transfer measurements, the effects o f precession (by ~ 10°) in the transverse plane could also be tested.Table I lists the values measured in this way for the normal and sideways proton polarizations at the po­larimeter. In the second column o f Table I are the val­ues expected on the basis o f the known analysing power for the time-reversed pp —* die reaction, corrected for the spin precession at the target. The excellent agree­ment between these two sets o f numbers confirms not only that systematic effects are well under control, but also that the analysing power o f the polarimeter (taken from values published by the Geneva group) is consis­tent with expectations based on analysing power mea­surements o f the inverse reaction.Analysis o f the spin-transfer results for the full data set obtained using the polarized target is now under way. So far, K ls results have been obtained for pion kinetic energies o f 105 and 205 MeV (corresponding to 500 and 700 MeV proton kinetic energy in the time- reversed reaction). These are: 0.078±0.038 at 9 =  32.5° (corresponding to 147.5° in the time-reversed reaction) and 0.198±0.029 at 6 =  34.5° (145.5° for the time- reversed reaction), respectively. The values expected on the basis o f Bugg’s partial-wave analysis are: 0.173 and 0.342, respectively.With this data included with the rest of the spin- dependent data for the inverse reaction, the extent to which the partial-wave amplitudes describing the reac­tion are constrained by these new results can be evalu­ated. An illustration is provided for the 105 MeV case in Fig. 21. Figure 23(a) shows how well the spin-cor- lation data measured by a number o f different groups23SIG find flssAnn fill filsKn.n Ks.s Kl.lKi.s Ks.l Ksn.sFig. 23. (a) Partial-wave amplitude fits to spin-correlation observables, (b) Spin-transfer parameters predicted by partial-wave amplitude fits.24ferent groups can be fit by different sets o f partial-wave amplitudes (in this case two solutions are shown, solu­tions which yield essentially equivalent x 2 values). In Fig. 23(b) the effect o f including our K ls  datum into the database is illustrated. One o f the original solutions (shown by the solid line) changes to that shown by the dashed line, a result which is more consistent with our measurement. Although the other solution (shown by the dashed-dot line) also “moves” toward the datum point, it is incapable o f yielding a good fit to our mea­surement without at the same time yielding a poor fit to the spin-correlation data. It is expected that, with the inclusion in the database of our results for K ss  and K n n  as well as K l s , all ambiguities o f this type in the partial-wave amplitude fits to the data will be resolved for the energies investigated.Experim ent 359Part II, M easurem ents o f the spin-flip probability  Sn„ for inclusive inelastic scattering o f 290 M e V  protons from  44 Ca(C. Glashausser, Rutgers; O. Hdusser, SFU/TRIUMF)Diffential cross sections (a), analysing powers A y , spin-flip probabilities 5nn, and spin-flip cross sections (’ ’Snn have been measured for the inelastic scattering of 290 MeV protons from 44Ca. Data were taken over the angular range from 3° to 12° in the laboratory (mo­mentum transfer q up to about 150 M eV /c) for energy losses w generally up to about 50 MeV, but extending to about 75 MeV at 7°. The S„„ measurement is de­signed to determine the relative spin response o f 44Ca, the percentage o f the 44Ca response to intermediate- energy protons which transfers spin (5 = 1 ) to the nu­cleus. Multipole decomposition o f the aSnn data de­termines the distribution o f spin excitation strength in the nucleus.The Snn data at 7° are shown in Fig. 24. They show the same features as Snn data for 40Ca at 319 MeV measured up to energy losses o f 40 MeV [Glashausser et al., Phys. Rev. Lett. 5 1 , 1526 (1987)]: small values o f Snn at low w, slowly increasing through the region o f 5 = 0  giant resonances around 18 MeV, and reach­ing a maximum of about 0.40 at high w. These val­ues reflect the predominance o f 5 = 0  correlations in the nucleus at low w, and 5 = 1  correlations at high w. The value o f 0.40 is considerably higher than the free value o f about 0.25, and indicates that the nuclear response is more than 80% 5= 1  at these excitation en­ergies. Such behaviour has now been seen for a num­ber o f nuclei between 12C and 90Zr in measurements both at TRIUMF and LAMPF [Baker et al, Rutgers Univ. preprint, in preparation]. The strong enhance­ment o f Snn at high excitations could not be explained-10 0 10 20 30 40 50 60 70 80 90Excitation Energy (MeV)Fig. 24. Spin-flip probability for inelastic scattering of 290 MeV protons from 44Ca at 7°.in calculations based on the response o f a semi-infinite nuclear slab with RPA correlations, although the qual­itative shape o f the spectrum was reasonably well de­scribed [Glaushausser et al, op. cit.] The data shown here were extended to 75 MeV to determine whether the enhancement disappeared if the excitation energy increased beyond the region where spin resonances are expected. Such a resonance -  which can be found in the multipole decomposition o f the crSnn data -  might reasonably be considered as the source of the enhance­ment, but by definition it should be moderately nar­row. The fact that Snn is approximately flat above 40 MeV indicates that some other explanation must be found. In Baker et a l, where these and other 5 „ „  data will be reported, fully microscopic RPA calculations by Castel and by Wambach are shown which suggest that the explanation o f the enhancement lies in the ex­haustion of 5 = 0  strength at lower excitation energies combined with some enhancement o f 5 = 1  strength at high excitation energies. Even these calculations, how­ever, are not yet satisfactory over the entire range o f q and w.A preliminary spectrum o f the a5 nn data at 3° is shown in Fig. 25. Some anomalies appeared in the ab­solute cross sections in the original run from which Fig. 25 is taken. New data taken this fall are cur­rently being analysed. Because the spin-flip probabil­ity for 5 = 0  resonances is essentially zero, and because the same is true for any instrumental background, this spectrum corresponds to the spectrum o f spin excita­tions in 44Ca. The strong bump near 20 MeV, very close to the position o f the 5 = 0  giant dipole resonance seen in the a spectrum, corresponds to the spin dipole in 44Ca. A weak structure on the low-energy side o f this2544Co(p,p') 290 MeV 3°Fig. 25. Spin-flip probability for inelastic scattering of 290 M eV protons from 44Ca at 7°.resonance at about 10 MeV is likely due to the excita­tion o f a weak M l resonance. This spectrum should be compared with similar data at the same angle taken in Part I o f this experiment for 54Fe, where an M l resonance is a very prominent feature [Hausser et al., in preparation]. Quantitative results for the strengths o f these states await a multipole decomposition which will be performed when the new absolute cross-section data are available.Experim ent 372Single-pion production in np scattering(N.E. Davison, Manitoba)The detection apparatus for Expt. 372 (np —^  ppn~) consists o f a charged particle tracking system, a time- of-flight system plus several systems for calibration and monitoring. The tracking system consists of 12 drift chamber planes, 4 each in the x, y and u directions, the latter at 45° to x  and y. The drift chambers cover the entire solid angle into which the two protons in the final state can be emitted. The TOF system consists o f a single TO F start detector and a segmented TOF stop array also covering the angles into which protons can be be emitted. Although the neutron beam passes through the central regions o f both the drift chamber and TOF systems, the coincidence requirements in the trigger reduce accidental false triggers to a negligible level.These detectors were installed in 1987 and tested in 1988. In addition, detectors were installed and modifi­cations made to the trigger electronics to 1) determine and monitor the efficiency o f all detectors, 2) determine during data acquisition, the alignment o f the appara­tus with respect to the neutron beam, 3) obtain a data sample with pions at large angles for testing the Monte Carlo simulations, 4) normalize the np —* ppir~ data to np elastic scattering, and 5) reduce false triggers due to events originating elsewhere than in the target.Since the np —► ppir~ reaction has three particles in the final state, all three analysing powers A x , A y and A z are in principle nonzero. It is therefore essential to know the polarization components o f the beam along all three co-ordinate axes. A second neutron polariza­tion monitor was therefore installed upstream o f the neutron spin precession dipoles to augment the exist­ing polarization monitor downstream o f the target.Experimental efforts during the past year have cen­tred around several short test runs plus a major test run in July, during which the full detection apparatus was brought up and tested with the goal o f obtaining high-quality data sufficient to test the data analysis programs and to enable decisions to be made concern­ing the fraction o f time to be spent acquiring data in the various trigger modes. Over the course o f the year, phase-restricted cyclotron operation was made “routine” with proton beam bursts o f less than 0.5 ns FWHM. A detection system was installed in the SFU chamber to monitor the width o f the proton burst and its phase with respect to the cyclotron rf. Software was written to run on the cyclotron VAX-730 computer for monitoring the proton beam burst and to transmit di­agnostic information to the MRS VAX-750 data acqui­sition computer.Data analysis programs are presently being devel­oped and tested against both real data obtained during the test runs and Monte Carlo data. Software for mon­itoring all crucial variables is being written to run con­currently with data acquisition on the MRS VAX, and a full analysis program including detailed maximum likelihood event reconstruction is being assembled to run on the cluster, receiving data over Ethernet for as many events as the cluster can analyse in real time.Experim ent 375Few -body physics with the -kd deuteron break-up  reaction (E.L. Mathie, Regina)Analysis o f the previously measured cross sections for 36 pion-proton angle pairs at 134, 180 and 228 MeV was extended to include an out-of-plane acceptance correction. This correction was extracted from the data, using the difference in time o f flight from the two ends o f the timing counter in each arm. This cor­rection factor is largest for those coincident arms lo­cated near the free pion-proton kinematical locus, and negligible for cases far from the quasifree region. A parasitic test was performed in July to confirm the26height (in time units) which was convoluted with the time-of-flight resolution for comparison with distribu­tions extracted from the data. W ith this correction ap­plied one finds typically good agreement with calcula­tions o f Garcilazo on the low-momentum side o f the distributions, up to 30% differences in the region of the quasifree peak, and frequent disagreements on the high-momentum side o f the distribution. Two publica­tions o f this work are in different stages o f preparation. The first discusses in detail the analysis technique with comparisons to other techniques previously used, and the second will discuss the energy dependence o f the cross sections.Measurements o f the vector analysing power for the same broad range o f phase space were completed in January using the TRIUMF polarized target. The ex­perimental technique involved measurements with the polarized target cell, a background cell and a polythene timing calibration target. As for the cross section ex­periment, a multi-arm time-of-flight arrangement was employed to register an event for 36 angle pairs o f pion and proton. Data analysis is under way, and prelimi­nary results should be available by summer o f 1989. This material will form part o f the Ph.D. work for Regina graduate student, D.M. Yeomans.Experim ent 394A bsolute 7r± p differential cross sections at low energies (G.R. Smith, TRIUMF)Angular distributions have been measured on the M il  and M13 beam lines at TRIUMF for both 7r +p and tt~p elastic scattering differential cross sections at incident pion energies o f 30, 45, and 67 MeV. Two techniques were used for tt+ p  at 67 MeV, one involv­ing passive targets (a single arm experiment), and the other using active scintillator targets to detect coinci­dent recoil particles. Measurements at the lower inci­dent energies were made using the active scintillator target technique only. The' cross sections were mea­sured at scattering angles ranging from 50° to 150° in the centre-of-mass system. Statistical uncertainties are typically 3% and absolute normalization errors 2%.The active target results were obtained in an experi­mental configuration consisting o f six two-element scin­tillation counter telescopes for detection o f the scat­tered pions. Data were thus acquired at six angles si­multaneously. The distance between the two scintilla­tors in a given telescope was varied as a check on our ability to reproduce multiple scattering and decay ef­fects by Monte-Carlo simulation. The active target was adjusted such that the trajectory o f recoil protons was in the plane o f the target. The correction for protons escaping from the surface o f the target, thus depositingec.m(deg )Fig. 26. The results o f the single-arm measurements at 66.8 M eV from this experiment are shown (solid points) together with the earlier results from Brack et al. (open points). The KH80 and W I87 phase-shift solutions at this energy are also plotted.less energy than expected, was studied in several ways, including the use o f a dual target system in which these escape corrections cancel, and by extensive variation of the target angle.At 67 MeV these measurements are in good agree­ment with earlier published data for both 7r+p and 7r~p  [Brack et al., Phys. Rev. 34, 1771 (1986); Phys. Rev. C 38, 2427 (1988)]. There is generally very good agreement between the measured cross sections for ir~ p and both the Karlsruhe (KH80) and the SAID (SM86) phase-shift solutions at all three energies, but the ir+p cross sections lie significantly below both phase-shift solutions at 45 and 67 MeV. The discrepancy for tt +p is typically several standard deviations.The results of the single-arm portion o f the experi­ment have just been published. The results of the active target portion o f the experiment are in the final stages o f analysis, which includes extensive Monte-Carlo cal­culations of the many different experimental geome­tries which were used as systematic checks. The final results will be available early in 1989.Experim ent 405Spin response o f m agnetic dipole transitions in 156G d  and 164Dy(D. Frekers, TRIUMF)Collective magnetic dipole transitions have recently been discovered in the deformed rare earth nuclei [Bohle et al., Phys. Lett. 137B, 27 (1984); Phys. Lett. 148B, 260 (1984); Nucl. Phys. A458 205 (1986)]. To generate these transitions, it is believed that proton and neutron deformed fluids perform rotational oscil­27lations against each other ( “nuclear scissor” ). The ex­citation constitutes an isovector M l transition, whose B(M1) value is dominated by convective current con­tributions. The properties o f such states have been well described using the two-fluid concept o f the interacting boson approximation (IBA), i.e. IBA-2.We have measured the M l transition in the ro­tational nuclei 164Dy and 156Gd using intermediate- energy proton scattering in order to assess the spin contamination. No significant spin strength (<2%  of the total strength) is found in 156Gd, whereas in 164Dy about 20% o f the total B(M1) strength is attributed to spin excitation.This difference between the spin response o f 156Gd and 164Dy is not expected within the framework of the IBA-2. The present results indicate that the un­derlying shell structure still has a prevailing effect. Such shell effects have been predicted by Nojarov and Faessler [Nucl. Phys. A484, 1 (1988)], who have performed RPA calculations for six rare earth nuclei (154Sm, 156,158Gd, 164Dy, 168Er, and 174Y b) using a self-consistent symmetry restoring quadrupole interac­tion. The calculated configurations lead to predomi­nantly orbital excitations, except for 164Dy , where the leading term is a two-proton quasiparticle spin-flip con­figuration o f the type [541] 1/2 —+ [541]3/2 (2/ 7/2 ~+ lh n / 2 ) resulting in a 90% spin admixture overall for the isovector Ml-transition. This is far larger than our experimental result, yet the observed difference be­tween 156Gd and 164Dy is in qualitative agreement. Since the above-mentioned configuration is also ac­tive in 158Gd, a similar experiment on this nucleus is planned.The work has been accepted for publication in Phys. Lett. B.Experim ent 413Cross sections and analysing powers for the 3He(p, x+ )4H e reaction in the energy range from  2 5 0 -5 1 5  M e V(W.R. Falk, K. Furutani, Manitoba)Beam time for this experiment was received in the fall, and detailed angular distributions o f the differ­ential cross sections and analysing powers were mea­sured at proton bombarding energies o f 300, 416 and 507 MeV. The present experiment was performed with the liquid 3He target and the medium resolution spec­trometer (MRS) using an achromatic beam of polar­ized protons and currents in the range from 4-35 nA. Use o f a dispersed beam with the 44 mm diameter cell would have been problematic and, moreover, was quite unnecessary, given the good peak-to-background ratio obtained in the spectra. The approximately 11 mmz 1® «®e 16® IS® *c 6® * ®te e  •e 6®A®E®•Fig. 27. Focal plane spectra o f the 3He(p, 7r+ )4He reaction.thick target cell represented a 3He areal target density o f 85 m g/cm 2 at a cell temperature just under 2 K.Figure 27 displays two focal plane spectra represen­tative of the range o f peak-to-background signals ob­served in the experiment. These spectra were recorded at a proton bombarding energy o f 507 MeV and a labo­ratory angle of 23° (top) and at 416 MeV and an angle o f 104° (bottom ). While the background is exceedingly small for the former spectrum, even the more signifi­cant background in the latter spectrum presents no difficulties in extracting the desired information. The background arises primarily from the 25.4 /im thick stainless steel windows on the liquid 3He cell. The sud­den rise in the spectra at high excitation corresponds to the opening up o f the channels associated with the excited states o f 4He.Comparison o f the angular distributions o f the dif­ferential cross sections with the data from the charge symmetric and time-reversed reaction 4He(7T_ , n )3H of Kallne et al. [Phys. Rev. C 24, 1102 (1981)] show good overall agreement. Similarly, the 415 MeV (p ,n + ) dif­ferential cross sections o f Tatischeff et al. [Phys. Lett. 63B , 158 (1976)] appear to be in good agreement with our 416 MeV results.While the differential cross sections display relatively little structure as a function o f angle, the analysing28powers, shown in Fig. 28, reveal large oscillations, the patterns o f which change markedly as the energy is changed. Previous investigations o f the analysing pow­ers o f this reaction were carried out at considerably lower energies (178 and 198 MeV) [Kehayias et al., Phys. Rev. C 33, 725 (1986)] and at a considerably higher energy (800 MeV) [Hoistad et al., Phys. Rev. C 29, 553 (1984)]. These results at 198 and 800 MeV are also shown in Fig. 28. Comparison o f the 198 and 300 MeV data reveals that the negative analysing power o f the lower-energy data -  characteristic o f the low-energy pp —► dn+ analysing power -  has changed character completely by the time the energy is in­creased to 300 MeV. The present 507 MeV data bears considerable similarity to the 800 MeV data, although the former has a more pronounced positive excursion at forward angles.Because spin-dependent observables provide par­ticularly stringent tests o f theoretical models, the present experiment has emphasized measurement of the analysing power in the A-resonance region where current microscopic models incorporating the two- nucleon mechanism involving intermediate A  forma­tion have their greatest validity [Alons et al., Nucl. Phys. A480, 413 (1988)].Experim ent 414M easurem ent o f the cross section for H(7r_ , x+ 7r_ )n very close to threshold(M.E. Sevior, UBC)Experiment 414 was awarded 15 shifts o f high- intensity beam to study the experimental set-up pro­posed to measure the total cross section for the reac­tion H(tt~ ,7T+ 7r- )n at energies between 176-200 MeV, which is between 4 to 28 MeV above threshold. At these low energies the total cross section for the reac­tion can be simply related to the value o f the chiral symmetry breaking parameter £. This is a very impor­tant parameter o f chiral perturbation theory as it de­scribes the nature o f the nonconservation o f the pion axial vector current [Olsson and Turner, Phys. Rev. 181, 2141 (1969)]. Recently chiral perturbation theory has been used to calculate the strange quark content of the proton and a value o f 40% was obtained [Weidner et al, Phys. Rev. Lett. 58, 648 (1987)]. The calculations assume a value o f 0 for £; however, the data generally believed to show that £=  0 were obtained at energies too far above threshold to be directly applicable and an extrapolation was needed to determine £[Bjork et al, Phys. Rev. Lett. 44, 62 (1980). There has never been a theoretical justification for the extrapolation and in fact a recent model of Oset and Vincente-Vacas [Nucl. Phys. A446, 584 (1985)] for the H(7t“ ,Tr+ Tr~)n reac-1.00.8 0.6 0.4 0.2 *  0.0 - 0.2 -0 .4  - 0.6 - 0.8 - 1.00 20 40 60 80 100 120 140 160 180ec* (deg)Fig. 28. Angular distributions o f the analysing powers.tion predicts that the low-energy dependence of the cross section is considerably different from the extrap­olation. Our measurement, to be made much closer to threshold, will avoid this extrapolation and provide a more reliable value o f the cross section at threshold and hence the definitive value o f the chiral symmetry breaking parameter.The major elements o f the experiment are shown in Fig. 29. The pion beam from M il  is counted by two beam-defining scintillators, SI and S2, placed up­stream o f the target. The size o f S2 was chosen so that its image on the target was 20x20 mm. The target con­sisted o f 3 scintillators o f dimensions 10x40x40 mm each viewed by a R1635 photomultiplier tube. Low- energy pions from the H (x_ ,7r+ 7r_ )nreaction are stopped within the scintillator target and the 7r+ ’s are identified by observing the 7r+ —► p + decay. Neutrons from the reaction were detected in coincidence by the neutron bars placed 2 m downstream at zero degrees. The energies o f the neutrons were determined by the time of flight o f the neutrons. The pion beam was swept clear o f the neutron bar scintillators with the PAC- MAN magnet.The goal o f this run was to test all elements o f the ex­perimental arrangement and demonstrate the feasibil­ity o f the technique. The 7r+ —> p + decay was detected in the active target by looking for the characteristic pulse from the 4.1 MeV muon stopping in the active target. The most definitive way o f doing this was to record the output from the phototubes in 2 ns incre­ments with a 500 Megasample per second transient dig­itizer. We used a TEKTRONICS 2440 digitizing scope to do this. The device worked admirably and enabled both the size and shape o f the active target output pulses to be readily analysed. To determine the accu­racy o f our knowledge o f detection efficiency for ir+ ’s stopped in the active target we stopped low-energy,He(p,7T^ ) He A nalyzin g  Pow ers(□ 8 0 0  MeV (LAM PF) a  5 07  MeV (TRIU M F) > 4 1 8  M eV (TRIU M F) . 3 0 0  MeV (TRIU M F) o  198 MeV (IU C F)29Fig. 29. The experimental layout to be used for the mea­surement.x + ’s from M il  in the active target. The results were compared with those obtained from runs at 184 MeV x~ when we were looking for the H (x_ ,x + x _ )n reac­tion. The detection efficiency o f the system is the num­ber o f counts in the “time o f second pulse” histogram divided by the area under the fitted 26 ns exponential decay curve. The precision o f the technique was deter­mined from the stopped x + runs where the number of 7r+ ’s stopped in the target was counted and compared to the number detected via their decay. Agreement at the 2% level was achieved, which was the statistical uncertainty o f the measurement. The double pulse de­tection efficiency achieved during the test run was 24%.The final spectrum of neutrons gated with a x + pulse in the active target is shown in Fig. 30. It was accumu­lated for the H (x_ ,7r+ x _ )n  reaction after 3 days o f run­ning a x~ beam at 184 MeV and rate o f 2 MHz. There is a clear enhancement o f the neutron energy spectrum in the region o f the H (x_ ,x+ x _ )nneutron energy peak as shown by the Monte-Carlo curve. The size of thebackground, (mainly due to the 12C (x _ ,x + n )X  reac­tion), was determined in a separate run at 172 MeV. This is just below threshold for the foreground run but still 140 MeV above threshold for the major back­ground reaction. These data were acquired during a run o f 1.5 days. The foreground-background subtrac­tion yields 640±90 counts in the energy range o f 15- 40 MeV, i.e. a statistical uncertainty o f 15%.The detection efficiency o f the neutron bars is de­termined by stopping low- energy x_ ’s in a liquid deu­terium target. The reaction, stopped i7~+d —► n+ri then occurs with a branching ratio o f 73% ±  1.0% [Highland et a l, Nucl. Phys. A303, 333 (1981)]. This reaction is used as a calibrated source o f monoenergetic, 70 MeV neutrons. A Monte-Carlo code was used to provide the energy dependence o f the detection efficiency o f the neutron bars given this one calibration point. In this way the neutron detection efficiency was calibrated to within 5%.We have submitted a new proposal to the TRIUMF EEC to make the full measurement. The changes to the existing arrangement are to construct a new ac­tive target consisting o f 5 scintillators each o f dimen­sions 6x40x40 mm, implement and test new double pulse detector hardware and acquire an additional two channels o f 500 MHz transient digitizer. None o f these activities will take more than 6 months and they can all be carried out in parallel. Therefore, we expect to be ready to take beam by the summer o f 1989. The final analysis o f the data will then take a further year.Fig. 30. The neutron energy distribution gated with x + events in the active target for the H(x~,x+ x~)ti reaction at 184 M eV. This spectrum was accumulated after 3 days o f running at an incident beam rate o f  2 x l0 6 pions per second. There is a clear enhancement in the energy range o f neutrons from the H (x _ ,x + x _ )n reaction as shown by the M onte-Carlo curve.30Experim ent 421Research and developm ent studies with T IS O L(J.M. D ’Auria, SFU; J. Vincent, TRIUMF)This brief report is intended to summarize progress achieved over the last twelve months for Expt. 421 and the TISOL facility. The goals o f this project are to de­velop and use the TISOL facility (the prototype, test on-line isotope separator) to address scientific and en­gineering questions o f importance to the ISAC (ISOL and accelerator) facility, and to develop TISOL as a useful physics facility.An early description of the TISOL facility was pre­sented in previous annual reports and is also given in Oxorn et al. [Nucl. Instrum. Methods B26, 143(1986)]. In 1987 this facility was installed and oper­ated successfully, as described in the 1987 Annual Re­port. During the past 12 months the end o f the TI­SOL line was extended and the mass separated ion beam taken from the vertical to the horizontal direc­tion. This brought the final collection point to a loca­tion o f much lower radiation background, allowing the detection of the collected radioisotopes while the pro­ton beam was on. The present layout o f the facility is shown in Fig. 31. The change in direction was achieved using electrostatic elements, namely six quadrupoles and a dipole. Further, additional steering devices were added along with diagnostic elements. This complete installation was completed during the summer, and a series o f runs made later in the year to survey the ra­dioisotopic production yields.El B enderFig. 31. A  schematic layout of TISOL.Table II. 1988 production yields (T i target -  1.5 g-cm 2).Isotope Z AT l /2(s)Production Yield*W  ionizer Re ionizerLi 8 0.844 2.8x 105 3.3x10s9 0.777 b bNa 20 0.446 1 .4 x l0 3 4.3x 10221 22.5 7.2x 104 -25 59.6 3.0x10s 6.1 x 10426 1.07 1.7 x 104 3.4x 10427 0.304 1 .5 x l0 3 4 .3 x l0 228 0.03 b bK 35 0.19 300 -36 0.34 1 .9 x l0 4 5.1x10s37 1.23 5.1x10s 3.0x10s38 458 3.3x 106 b42 12.36 h 9 .6 x l0 7 b47 17.5 b 4 .5 x l0 3*units: ions ■ s 1 ■ fiA 1 incident phobserved but yield not measuredTwo experimental set-ups are used to measure yields. In both arrangements a fixed collector is viewed with a Ge(Li) 7 spectrometer, a Si surface barrier charged particle detector, an E -E  plastic telescope (for energetic /3’s and a high gas pressure, 3He fast neu­tron spectrometer (from McGill). In one arrangement the ion beam is simply stopped and the emitted ra­diations studied. In the second (for ms and s activ­ities) the ion beam is deflected electrostatically and cycled, synchronized with the data-acquisition system. All spectra data were collected with a PA 8000, MCA board in an IBM (clone)-AT. The first results are pre­sented in Table II. O f interest here are the observations and measurements o f rather short-lived species. In gen­eral these yields are comparable to values obtained at the ISOLDE facility (CERN) when normalized for tar­get thicknesses. Slightly lower yields are attributed to the smaller extraction voltage, the lower temperature achieved in the heated surface ion source at TISOL, and transmission loss through magnetic quadrupoles used after the extraction electrode. Design changes are in progress to improve the latter two points. In addi­tion to these results, runs were attempted with Ta foil targets, but these were not successful due to the much higher temperatures needed for the ionizer (2500°C) and target oven (2200° C).Ion source developments were achieved in three main areas. Following an essentially unsuccessful run with an all-graphite system (oven and plasma chamber), a novel compact electron heating, plasma source was31signed and is presently under engineering development. A second-generation surface ion source was installed and successfully operated. This is a more robust source, capable o f handling higher temperatures and could be used as a production source. Finally, an off-line elec­tron cyclotron resonance (ECR) ion source and mass analyser system was assembled and tested successfully. Singly charged ion beams o f oxygen, nitrogen and re­lated gaseous species were extracted. Measurements are in progress this year on the observed ionization effi­ciencies for single and multiple charged ions o f a range o f low Z gaseous elements. These are being performed in collaboration with G. Roy o f the Univ. o f Alberta and his graduate student, P. McNeely.In summary, TISOL is now a facility that can be used almost routinely for the measurement of produc­tion yields o f a limited range of radioisotopes.Experim ent 430Spin excitations in 208 Pb(C . Glashausser, Rutgers; C.A. Miller, TRIUM F)This experiment was designed to measure the spin- flip probability Snn for inelastic scattering of 200 MeV protons from 208Pb to determine the strength o f spin resonances, particularly the M l, and to look for evi­dence of the enhancement o f Snn relative to the free N N  values at high energy loss u>. In the first phase, which was essentially a feasibility study, ten shifts were devoted to measurements at 4°, 6°, and 8°; the results are discussed below in detail. They revealed large val­ues o f Snn in the M l region, clear evidence for a spin dipole resonance, likely evidence for a spin quadrupole in the 15-25 MeV region, and some tantalizingly low values o f Snn in the high w region where statistics are poor. Up to 35 MeV, statistics were typically ±0.08 on Snn in 1 MeV bins.Data from Phase I for inelastic scattering of 200 MeV protons from 208Pb are shown in Figs. 32-34. The dom­inant feature in the 4° spin-flip cross section (crSnn) spectrum in Fig. 32(a) is the clear spin dipole reso­nance in the 10-15 MeV region. The tail o f this reso­nance extends into the likely M l region around 7 MeV. It also extends into the high excitation energy region where the 6° and 8° (rSnn spectra in Figs. 32(b) and 32(c) show a bump between 15 and 25 MeV which very preliminary analysis suggests is primarily the spin quadrupole resonance. Absolute values o f crSnn for 208Pb are roughly similar to those measured previously for medium weight nuclei.The data for Snn indicate values above 0.2 in the M l region below 10 MeV at 4° in Fig. 33(a). These values are surprisingly large, given the clear tail of the non-spin-flip El resonance which extends into thisa) _  208Pb(p,p') 200 MeV 4°^  3.0 2^ 2 .5  .o Ew  2.0 c08 1.5 co 0)8 1.0o.9- 0.5Ll.1•| 0.0w 0 5 10 15 20 25 30 35 40Excitation Energy (MeV)Fig. 3 2 (a )-(c ). Spin-flip differential cross sections (da/dU S„n) for proton inelastic scattering on 208Pb at the angles and energies indicated.region as seen in the 4° u data in Fig. 34(a). The gamma ray data o f Laszewski et al. [Phys. Rev. Lett. 54, 530 (1985)] and the previous (p,p') cr data from Or- say [Djalllali et al., Phys. Rev. C 31, 758 (1985)] also suggest that the E l is large here. The large value of Snn indicates significant spin-excitation strength here,32Pb(p,p‘) 200 MeV ~rPb(p,p') 200 MeV ~r0.0b)5 10 15 20 25 30 35 40Excitation Energy (MeV)208Pb(p,p') 200 MeV 6°Excitation Energy (MeV)Excitation Energy (MeV)Fig. 3 3 (a )-(c ). Spin-flip probabilities for proton inelastic scattering on 208Pb at the angles and energies indicated.b)10 15 20 25 30Excitation Energy (MeV)’PbCp.p') 200 MeVExcitation Energy (MeV)208 P b (p .p ')  2 0 0  MeVExc i ta t ion  Energy (MeV)Fig. 3 4 (a )-(c ). Differential cross sections for proton inelas­tic scattering on 208 Pb at the angles and energies indicated.but the fact that Snn remains high at 6° and 8° in this region indicates that not all o f this strength is M l. In the spin-dipole region, 10-15 MeV, Snn at 4° is signif­icantly smaller than in the M l region even though the spin-dipole resonance dominates the entire (rSnn spec­trum at 4°. The small values o f Snn here occur becauseo f the enormous cross section for the Coulomb-excited E l in the cr spectrum. Snn increases again at all an­gles in the 20 MeV region and tends to stay high up to 35 MeV where the polarimeter efficiency de­creases markedly. The data at higher u  thus have very large error bars, but there is some indication that the33average values are somewhat below the enhanced val­ues o f 0.4 seen in this w region for medium weight nuclei [Glashausser et al. [Phys. Rev. Lett. 58, 2404 (1987)].The cross section spectra show a bump in the 20- 25 MeV region at all three angles. Previous reports on cross section measurements in this region [Lisantti, thesis, Univ. o f Oregon, 1986] propose that this bump corresponds to the giant 5 = 0  octupole resonance. It is interesting to note, however, that a featureless back­ground has been assumed in that work. The present data show a bump in the <r5„n spectra in just this region. As shown by our previous work on 40Ca, the crSnn spectra (multiplied by the appropriate factor, typically about 2) give a much better estimate of the “background” to subtract when extracting 5 = 0  res­onance parameters than the phenomenological back­grounds previously assumed [Baker et al., Phys. Rev. C 37rc, 1350 (1988)] will be important to determine whether the “5 = 0  octupole resonance” remains after subtraction o f a background which includes the appar­ent spin quadrupole resonance.In 1988 we have used a further 20 shifts o f beam time in an effort to obtain definitive evidence on the spin-dipole and spin-quadrupole resonances, as well as on the enhancement o f Snn over the free values. The improved statistics in the M l region are not expected to be sufficient for a definitive M 1/M 2 separation, but it is hoped that they will yield a useful limit on the M l strength in the low excitation region.E x p e r im e n t  432P o la r iz a t io n  tra n sfe r  in  in e la stic  p r o to n  s ca tte r in g  fr o m  16 O(B. Larsen, Simon Fraser; O. Hdusser, TRIUMF/SFU; R. Jeppesen (L A M P F ); D. Frekers, TRIUM F)The aim o f Expt. 432 is a test o f the effective in­teraction o f intermediate-energy protons with the nu­cleus. This is accomplished by measuring cross sec­tions and a complete set o f spin observables for the reaction 160 (p ,p ') . The “stretched” 4~ states in 160, at excitation energies o f 17.79 MeV, 19.80 MeV (both mainly T = 0 ) and 18.98 MeV (almost purely T = l ) ,  are strongly populated by this reaction. They are char­acterized by a dominant particle-hole configuration (p ^ 2d5/2) and an isospin structure determined previ­ously from electron [Lingren and Petrovich, in Spin Ex­citations in Nuclei (Plenum, New York, 1984), p. 323] and pion [Holtcamp et al., Phys. Rev. Lett. 45, 420 (1980)] scattering experiments. Stretched states pro­vide a useful nuclear filter to examine spin-dependent components o f the complex (10-piece) effective N- nucleus interaction. For the range o f momentum trans­fers where the 4~ states are strongly excited (q ~  1.3-2.5 fm_1) the isoscalar interaction has contributions from both tensor and spin-orbit terms, whereas the isovector interaction is dominated by the tensor force. Although the relative strength o f both isoscalar compo­nents may vary greatly (the tensor part is much more prominent in the density-dependent Paris-Hamburg G matrix [Rikus and von Geramb, Nucl. Phys. A426, 496 (1984)] than in the free f-matrix o f Franey and Love Phys. Rev. C 31, 488 (1985)] very similar differential cross sections (cr) and analysing powers (A y) may re­sult. Measurements o f cr, A y are therefore of limited use in unravelling the isoscalar interaction. The spin transfer coefficients Dip provide a considerably more sensitive test o f the interaction.The experiment was carried out using polarized pro­ton beams in BL4B. Protons scattered off a waterfall target developed at Univ. o f Toronto were momen­tum analysed with the medium-resolution spectrome­ter (MRS). The transverse spin components o f the pro­tons were determined by secondary inclusive scatter­ing from carbon using the MRS focal-plane polarime- ter (FPP). A total o f 16 shifts o f polarized beam time were consumed to determine cross sections, analysing powers, induced polarization and spin transfer coeffi­cients D ,si and D sp at 350 MeV. In addition, cross sections and analysing powers were measured at 290 MeV. Cross sections measured at 200 MeV were found to be in good agreement with those from previous work at IUCF [Olmer et al., to be published], A further 22 shifts will be required to complete the set o f spin ob­servables at 350 MeV by determining D nn, Dw and D h'.In Fig. 35 we show the spectrum quality obtained with the waterfall target. The resolution during long runs was typically only 140 keV whereas the intrin­sic resolution of the MRS determined with a thin Pb target was 70 keV. The 4 " states are superimposed onChannel NumberFig. 35. A typical MRS H2 O spectrum taken using the Univ. o f Toronto “waterfall” target.34is 0(p,p')180* Tinc=350MeV------------------  = SP84--------------------  GPH16 0(p,p')160* ^nc =350MeV------------------  = Peaks + Backgroundo— ------------------   Background Q  —uXC5"e'b"ee c.m. (deg.)O'LO0.6OQ 0 St-0  St - 0.6 -LOT ---1--- (... ... —,----------—1 ■ "  1 T - 17 16 10 20 21 22Excitation energy (M eV )Fig. 36. Angular distributions for the three 4 states in 160 ,  compared with various theoretical models (see text).Fig. 37. The raw data binned in excitation energy at b 22°. The peak-fitted results are shown for comparison.a substantial continuous physical “background’1 which arises from quasielastic scattering. In Fig. 36 angular distributions for the three states are compared to pre­dictions corresponding to the free f-matrix o f Franey and Love [op. cit.] (solid lines) and to the G-matrix of von Geramb [op. cit] (dot-dashed lines). Calculations using the G-matrix o f Nakayama and Love [Nakayama et al., Nucl. Phys. A431, 419 (1984)] and the rela- tivistic model o f ,/V-nucleus scattering developed at Colorado [Rost and Shepard, computer code DREX, preprint and private communication] give qualitatively similar predictions and are not shown.The systematic errors implied in separating the 4“  peaks from the underlying background can be judged from the 22° results shown in Fig. 37. The raw data summed in bins of 0.2 MeV o f excitation energy are shown as open points, the solid points are for the discrete 4~ states. The dashed lines correspond to a smooth representation of the background, whereas the solid lines include also broad features included in the Gaussian peak fitting program. In addition to D ss< and D,ii we have combined the data in a check relation­ship Css' which should vanish within statistical errors and which provides a useful test o f the reliability of35“ 0(p,p')“0 - Tino=350MeV-----------------------  = SP84-------------------------  GPHFig. 38. Angular distributions o f D slli for the three 4 states.the FPP results. From results of the type shown in Fig. 37, and from the variation of the answers for the observables using a variety o f peakshapes compatible with the observed shapes o f background-free discrete peaks at low excitation, we estimate an upper limit of < 0.1 for the systematic errors in the spin observables for the discrete 4“  states.The results for D ssi and D si' shown in Figs. 38 and 39, respectively, include statistical errors only. We no­tice several discrepancies between the experiment and any o f the (four) theoretical predictions which are out­side o f likely systematic errors. The zero crossing ofie0(p,p')160' Tinc=350MeV-----------------------  = SP84-------------------------  GPHFig. 39. Angular distributions of D for the three “stretched” states in 160 .D s$i for the 18.98 MeV T = 1  state is shifted to larger angles than predicted. The zero crossing occurs in the plane-wave impulse approximation (PW IA) at a mo­mentum transfer where the longitudinal and transverse pieces of the isovector tensor interaction are equal and is relatively unaffected when exchange and distortions are included. This result could be confirmed with a measurement of Dw  which should assume values of - 0.5 when V 1 «  V 1.The theoretical predictions for D s\‘ for the two (mainly) T —0 states are considerably above the data. It is at present not clear whether this indicates a de­36feet o f the effective interactions (or the N N  data base which underlies these interactions), or whether uncer­tainties in the nuclear structure o f the 4~ states are major contributors.An interesting byproduct o f the present experiment, the spin observables for the quasielastic ‘background’ at a fixed u> =  17-22 MeV can be used to test cur­rent models o f quasielastic scattering. The data set, once complete, will provide information on the q- dependence o f the spin observables and complement existing data sets at 500 MeV [Carey et al., Phys. Rev. Lett. 53, 144 (1984)] and 290 MeV [Hausser ei al., Phys. Rev. Lett. 61, 822 (1988)].Experim ent 435Spin-flip probabilities with the (p , n) reactions (R. Helmer, TRIUMF)The study o f spin transfer in the 54Fe(p, n )54Co* re­action completed 16 shifts of data-taking in Septem­ber. The measurement was carried out on the TRI­UMF charge exchange facility [Helmer, Can. J. Phys. 65, 588 (1987)]. The neutrons were counted by detect­ing recoil protons from a hydrogenous liquid scintilla­tor (BC 513) contained in a glass cell (2.54 cm wide x 5.08 cm thick x 7.0 cm high); their polarization was determined by making use o f the analysing power of the H(n, p) reaction and flipping the spin of the inci­dent protons. The recoil protons were detected by the MRS positioned at a scattering angle o f 27°, where the product o f H(n, p) cross section times analysing power squared (the usual figure o f merit for analysing power measurements) is a maximum. A signal derived from a photomultiplier tube which was viewing the converter was used to correct the focal plane position for the energy loss of the protons in the converter. The en­ergy resolution achieved on line was ~3.5 MeV. The effective analysing power o f the scintillator/MRS com­bination was calibrated using polarized neutrons from the 7Li(p, n )7Be reaction whose spin transfer coefficient D nn is known [Taddeucci et al., Phys. Rev. Lett. 52, 1960 (1984)].Analysis is in progress.Experim ent 441Analysing powers in 7r± p elastic scattering  between 98 and 263 M e V  (G.R. Smith, TRIUMF)A series o f measurements o f iT+p and ir~p elastic scattering from a polarized proton target was per­formed on the M il  beam line at TRIUMF in January. The detection apparatus was the TOF spectrometer. The goal o f the experiment was to obtain precise values o f the 7r p  analysing power A(9) over a systematic seto f angles and bombarding energies spanning the region o f the (3,3) resonance. Measurements o f this observable are crucial ingredients in determining accurately the 7rN  phases. A(9) consists o f an interference between different amplitudes, and is therefore sensitive even to nonresonant phases. Since very few A{9) data existed previously in the energy range o f this experiment, par­ticularly for 7r~p, these data will help considerably to restrict the acceptable phase-shift solutions for the irN interaction.The TRIUMF polarized deuteron target was em­ployed for the experiment, charged with normal bu­tanol (C4H9OH) target material in a frozen spin mode at 1.25 T. The polarizing magnetic field (2.5 T ) was in the vertical direction. The average target polariza­tion was 70.5%, as measured using an NMR technique before and after each run.The scattered pion and recoil proton were de­tected in coincidence using a time-of-flight scintillation counter telescope spectrometer developed specifically for these type o f measurements, and described in detail elsewhere [Smith et al., Phys. Rev C 35, 2343 (1987); Brack et al., Phys. Rev. C 34, 1771 (1986)]. Six sets o f pion and proton detectors were used so that data could be acquired simultaneously at six angles. Data were acquired in two angular settings of the detectors (12 angles in total) ranging from 50° to 140°. The inci­dent pion energies at the centre o f the polarized target were 98, 138, 166, 214 and 263 MeV. The pion beam flux was determined directly with two in-beam coin­cident scintillators. The pion fraction o f the incident beam was determined for each run by TOF through the channel using a beam sample circuit.Sufficient data were accumulated to provide uncer­tainties on the asymmetry o f 0.01 or less for n+p and 0.04 or less for tt~p. The effect of the new A(8) data on the phase-shift analyses was determined using the pro­gram SAID [Arndt and Roper, SAID on-line program]. Single energy analyses were first performed at 5 ener­gies from 100 MeV to 250 MeV. The S- and P -wave phase shifts were derived from these fits. The new mea­surements were then included in the data base and the analyses were repeated. The predictions o f analysing powers from the “old” and the “new” solutions is com­pared to the data at Tw =  166 MeV in Fig. 40.At all energies there is a considerable reduction in the uncertainties o f A(Q) but it is most pronounced for 7r~p. At 166 MeV, for example, the uncertainties in A(9) for 7r~p are reduced by a factor of between 10 and 20 at most angles. Changes in the actual predictions are also most pronounced for 7r~p  between 138 and 214 MeV.The effect on the phase shifts is largely a substan­tial reduction o f the uncertainties, with a less dramatic37CM Angle (D eg rees)CM Angle (Deg rees)Fig. 40. The 7r+p (upper) and n~p (lower) A(d) data from this experiment are shown. The “old” predictions of A(0) are indicated by the vertical bands, the extent of which represents the uncertainties associated with the old predic­tions. The “new” solutions which encompass the new data are plotted as solid lines, bounded by the uncertainties in­dicated by the dashed lines. From this figure, representative of the data obtained in this experiment, there is clearly a dramatic improvement in our knowledge of the itN phases, especially for t~p.effect on the obtained values themselves. The largest effect is on the 1=  1/2 waves (S n , P\i and Pi 3) where the uncertainties are reduced on some partial waves by a factor o f 10 or more. The new A(9) data have been included in the data base used for SM88 [Arndt and Roper, op. cit.\.Experim ents 442 , 443The A(-k , 2tv)A ' reaction above threshold(R. Rui, N. Grion, Trieste)The A (7r, 2v)A ' research program has continued ex­amining the 2H and 208Pb nuclei at Tn+ =  280 MeV. Data were taken in summer during a period of high- intensity beam. As a part o f the same program, in 1987 the 160  target was studied at the same energy. These experimental results and their comparison withthe available theoretical models will direct, for the first time, our understanding in the realm o f the A  depen­dence of the (7r, 2ir) process in complex nuclei.In the case of 160  our results [Phys. Rev. Lett. 59, 1080 (1987) and Nucl. Phys. A (in press)] were com­pared with the predictions of the model of Oset and Vicente-Vacas [Nucl. Phys. A454, 637 (1986)], and the most important findings were:• the total cross section increases sizably, 2.5 to 3, when using the dispersion relation o f pions in the nuclear medium instead of the free one, and• no precritical inhancement were detected as they were suggested in a work of Cohen and Eisenberg [Nucl. Phys. A395, 389 (1983)].Analysis on 2H has almost been completed and shortly a full-length paper describing the observed fea­tures will be submitted for publication in collabora­tion with M. Vincente-Vacas. The 20SPb target was not fully examined in the runs this summer. We were able to cover slightly more than 1/2 of the allowed in the reaction plane phase-space. Data-taking on this target will be completed in 1989. However, the set of data in our possession already represents a stringent test for the A(7r,27r)A' model originally proposed by Oset and Vicente-Vacas and successively modified by Vicente-Vacas to account for N  ^  Z  nuclei [private communication].In order to ensure a unique identification o f the re­action products, the experiment required a coincidence between final-state negative and positive pions. The apparatus used to detect 7r~ tt+ pairs consists of the TRIUMF QQD magnetic spectrometer which analysed negative pions, and the CARUZ, a scintillator total absorption range telescope which mass identified pos­itive pions. The incident beam was monitored by two hodoscopes. A hodoscope o f four scintillators placed downstream from the target monitored the spatial po­sition and intensity o f the pion flux at the target lo­cation. Likewise, a high-rate multiwire proportional chamber mounted upstream of the target measured the flux and the x-distribution of the pion beam. For the 2H(7T+ , 7T+ 7r_ )pp measurement a LD2 cylindrical target o f 2 in. diameter and 2 in. height was used. In order to avoid background measurements because of the pres­ence of the target cells, raytracing o f the incoming and outgoing pions was necessary. Figure 41 shows the re­sults o f a run with empty target. The rim of the vessel is clearly visible allowing for unambiguous target cuts.Measured many-fold differential cross sections are presented in Figs. 42, 43 and 44. The full and dashed curves are a Monte-Carlo phase-space simulation of the ( 1) nn —+ 7T7rp and (2) nd —+ mrpp reactions, respec-38Fig. 41. The Q Q D  wire chamber traceback to the empty LD 2 target.tively. Simulations carry the same kinematical cuts as the experimental data, and they are normalized to the data o f Fig. 42. Figure 43 shows a triple-differential cross section as a function o f the kinetic energy of neg­ative pions. As far as the Monte-Carlo simulations are concerned, comparison to the data of Fig. 43 suggests that the reaction, for this subset o f data, proceeds via the elementary 7rN  —* 2irN process, while the second nucleon o f the deuterium acts as a spectator. Finally, large deviations from the data are shown in Fig. 44 for both reaction channels, (1) and (2). This subset of data indicates that only pure phase-space considerations are not adequate to interpret the data, and a microscopi­cal description o f the process is necessary [Nucl. Phys. A446, 584 (1985)].bm"a0V+ (degrees)Fig. 42. The measured threefold differential cross section (open squares) as a function o f the angle o f positive pions. The full and dashed curves are Monte Carlo phase-space simulation o f  the xn —* imp and 7rd —► rnrpp reactions, respectively.Fig. 43. The measured threefold differential cross section (open squares) as a function o f the kinetic energy of nega­tive pions. The curves have the same meaning as in Fig. 42.The total cross section for 160  was obtained by inte­grating the four-fold differential cross section over the energies and angles of the 7r+ 7r~ pairs. The value found was 2.25±0.35 pb. The same procedure was employed for 2H, and the preliminary value is about 5 times lower than that for oxygen in good agreement with previ­ous published LAMPF data [Phys. Rev. Lett. 53, 540(1984) and Phys. Rev. C 33, 655 (1986)].>-OCh+E-h*"b1Eh-eCl"eG"eb"b? ;+  (MeV)Fig. 44. The measured fourfold differential cross section (open squares) as a function of the kinetic energy of positive pions. The curves have the same meaning as in Fig. 42.39Fig. 45. Experimental layout of the bremsstrahlung experiment.Experim ent 446  Pion-proton brem sstrahlung(P. Kitching, TRIUMF/Alberta; A. Stetz, Oregon State)The reaction irp —> irpy was first studied with the expectation o f measuring the magnetic moment o f the A ++ resonance. A model analysed by Kondratyuk and Ponomarev predicted that the bremsstrahlung photons fron the pion and proton would interfere destructively at backward photon angles and that the cross sec­tion d5a/dClndQ-ydk would have a large bump around k fa 70 MeV corresponding to the excitation of the A(1232). A group from UCLA working at the 184-inch cyclotron pursued this idea in a series of experiments during the 1970s. The data, however, were found to decrease smoothly like l/k in contrast with theoretical calculations. The UCLA group explored a wide range of kinematic conditions, but no sign o f the A  was seen. This has posed a theoretical puzzle, which has not yet been completely solved.Experiment 446 is intended as a survey experiment to collect differential cross section and asymmetry in­formation for the reaction it+p —> n+p j  from a po­larized target over a wide region o f phase space. The experimental set-up is shown in Fig. 45. The pions will be detected with the PACMAN spectrometer using a new set o f drift chambers. Photons will be detected in three Nal detectors: TINA, MINA and a new, smaller detector on loan from the Univ. of Alberta. The protonenergy and angle will be determined by a segmented array of plastic scintillators currently under construc­tion at Oregon State University.The experiment is scheduled to begin data-taking during January 1989. The initial run will concentrate on 265 MeV incident pion energy and the photon an­gles 60°, 105°, 150° and 220°, as shown in Fig. 45.Experiment 459Excitation o f the 10.957 M e V  0 ~ ,T = 0  state in 16O by 200 and 400 M e V  protons(J.D. King, Toronto; D. Frekers, TRIUMF; R. Schubank, Saskatchewan)In proton physics the 0+ —+ 0“  transition offers a number of interesting aspects. Being an unnatural par­ity transition it requires a spin flip, but at the same time the complexities o f both the nuclear structure and nuclear reaction are greatly reduced because only J—0 states are involved. In particular, with the spin- orbit part o f the effective interaction not contributing and the central part predicted to be weak [Love et al., Proc. Int. Conf. on Spin Excitations, Telluride, 1982 (Plenum, New York, 1984), p. 205], the transition effec­tively probes the tensor part o f the nucleon- nucleus in­teraction, which is the least well-known piece. Further, it has been shown [Zhu et al., Nucl. Phys. A439, 619(1985)] that in a nonrelativistic frame the analysing40Fig. 46. Cross section and analysing power data for the 0+ —*■ 0-  transition in 16 O for (a) 200 M eV (b) 400 MeV incident proton energy. The full line represents a calculation using the Hamburg density-dependent interaction, the dashed line a Love-Franey interaction. The dotted line is a relativistic D REX  calculation.power A y can only take nonzero values as a result of the exchange parts o f the interaction. This is notably dif­ferent from a relativistic calculation where nonzero val­ues for A y are possible without the explicit inclusion of exchange [Piekarewicz, Phys. Rev. C 35, 675 (1987)]. It is, however, also necessary to include exchange contri­butions, and a microscopic distorted-wave relativistic impulse approximation with explicit exchange (DREX) has been formulated [Rost and Shepard, Phys. Rev. C 35, 681 (1987)].We have chosen the 10.957 MeV T —0 state in 160  for our measurement since the resolution with dispersion matching o f the MRS seemed adequate.Measurements o f differential cross section and analysing power were made for incident protons of 200 and 400 MeV. At 200 MeV, a BeO target o f approxi­mately 80 m g/cm 2 was used initially. Since the 0“  state is only weakly excited, it was difficult to extract this peak from the Be background and the strongly excited 4+ state in 160  139 keV higher in energy. A waterfall target was constructed based on a design o f such a tar­get for electron scattering [Voegler and Friedrich, Nucl. Instrum. Methods 198, 293 (1982)]. This target was used successfully at both 200 and 400 MeV. However, even with the improved background from the waterfall target, it was not possible to extract the 0_ state fromthe spectrum at angles greater than 32.5° at 200 MeV and for angles greater than 14° at 400 MeV with the best resolution o f 140 keV.The differential cross section was determined by nor­malization to the elastic cross section which has been measured at TRIUMF [Chan, Univ. of Alberta M.Sc. thesis (1985) unpublished] and IUCF [Glover et al., Phys. Rev. C 31, 1 (1985)].Cross section and analysing power data are shown for 200 MeV in Fig. 46(a) and for 400 MeV in Fig. 46(b). Also shown are nonrelativistic impulse ap­proximation calculations using the Hamburg density- dependent interaction [von Geramb, AIPCP No. 97 (AIP, New York, 1983), p. 44] (solid line), and the Love-Franey effective interaction [Love and Franey, Phys. Rev. C 24, 1073 (1981); 31, 488 (1985)] (dashed line), as well as a DREX calculation (dotted line). None o f the calculations provides a good fit to the data. In particular, the analysing power at forward angles is less than predicted and there is an indication at 400 MeV that it may even become negative.All of the calculations shown in Fig. 46 have as­sumed that the 10.957 MeV state is a pure T = 0 state. However, many states in 160  are known to be isospin mixed, and mixing o f 5-10% between the 10.957 MeV T = 0 and 12.979 MeV T =  1 states has been suggested41[Barker, Aust. J. Phys. 31, 27 (1978)]. Preliminary cal­culations show that the inclusion o f mixing indeed de­presses the analysing power for angles less than 5° at both 200 and 400 MeV.Clearly, more forward angle data are required at both energies. The waterfall target is not suitable for use near zero degree because o f scattering from the win­dows, and a solid target like BeO or H310BO3 o f about 10 m g/cm 2 is preferable. The latter has been success­fully used in a recent IUCF experiment [Sawafta, ex­perimental proposal, 1988]. Resolution requirements are not as stringent, since the nearby 4+ state is only very weakly excited at very forward angles.Experim ent 466M easurem ent o f np —^ dx0 cross sections near threshold (D .A. Hutcheon, TRIUMF)The experiment had a very successful production run in August, this time using a 1.5 cm thin liquid hydro­gen target. The aim o f the experiment is to make a precision measurement o f the total cross section for the np —► dir0 reaction at energies very close to threshold. Using the Chargex facility to get a neutron beam of good energy resolution and detecting recoil deuterons in singles in the MRS spectrometer, we were able to see clearly above background the locus o f the desired two- body reaction even at an energy 1 MeV lab (0.5 MeV c.m.) above threshold.The yield o f deuterons will be normalized to the yield o f protons from np elastic scattering, these knock-on protons being accumulated at the same time as the deuterons. It is necessary, therefore, to know accu­rately the relative acceptances o f the MRS for protons and deuterons. This part o f the analysis has been com­pleted and the final stage, fitting o f the deuteron yields to obtain the dependence o f np —* dir0 cross section on reaction angle and beam energy, has begun.Experim ent 468G am ow -Teller transitions to isospin triads in A = 6 ,1 2  nuclei studied by (n ,p ), (p, p') and (p, n) reactions at 280 M e V  (J. Mildenberger, Simon Fraser; 0. Hdusser, SFU/TRIUMF)The original motivation for this experiment was to provide an accurate determination o f isospin violation for the Gamow Teller matrix elements connecting the ®Li (T = 0 , Jr =  1+ ) ground state with the T = l ,  « /*=  0+ isospin triad in 6He, 6Li and 6Be. The forward-angle cross sections for the (n ,p ), (p, p') and (p ,n ) reactions are proportional to the square o f the matrix element of the aTq operator (q =  — , 0 ,- f ) , with the proportional­ity constant determined by the f t  value for the 6He /?“  decay. The G T  matrix element in 6Li can then be com­pared to the M l matrix element known from 6Li(e, e') experiments [Bergstrom et al., Nucl. Phys. A317, 439 (1979)]. The M l and G T matrix elements are domi­nated by identical spin parts but differ by meson ex­change current (MEC) and orbital contributions, the latter being absent in the G T matrix element. Both the orbital and MEC effects can be reliably calculated in a light nucleus such as 6Li, and any residual discrepen- cies between the axial vector and M l matrix elements might then be ascribed to a change in the size o f the nu­cleon inside the nucleus (an EMC-related effect). Such an interpretation is compatible with the cloudy bag model in which the magnetic moment o f the nucleon scales with the radius of the bag, while the axial vector coupling remains roughly constant.We report here forward-angle measurements of (n ,p ), (p ,p ') and (p, n) cross sections at 280 MeV us­ing the medium resolution spectrometer (MRS) and the CHARGEX facility. To our knowledge this is the first attempt to determine isospin violation in the three reactions. In addition to the A =6 data we have mea­sured cross sections for similar transitions to the A =12 triplet. The A =12 triplet has been studied extensively both theoretically and experimentally and serves as a test o f our experimental techniques