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

Annual report scientific activities, 1989 TRIUMF Oct 31, 1990

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
51833-TRI-Annual Report-1989.pdf [ 113.52MB ]
Metadata
JSON: 51833-1.0107786.json
JSON-LD: 51833-1.0107786-ld.json
RDF/XML (Pretty): 51833-1.0107786-rdf.xml
RDF/JSON: 51833-1.0107786-rdf.json
Turtle: 51833-1.0107786-turtle.txt
N-Triples: 51833-1.0107786-rdf-ntriples.txt
Original Record: 51833-1.0107786-source.json
Full Text
51833-1.0107786-fulltext.txt
Citation
51833-1.0107786.ris

Full Text

TRIUMFANNUAL REPORT SCIENTIFIC ACTIVITIES 1989CANADA’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 1990.TRIUMFANNUAL REPORT SCIENTIFIC ACTIVITIES 1989TRIUMF4004 WESBROOK MALL VANCOUVER, B.C. CANADA V6T 2A3E X IS T IN GP R O P O S E DPR O TO N  HALL E X T E N S IO NREMOTH A N D LFACILITSERVICEBRIDGESERVICEA N N E XE X TE N S IO NH POLAI IO N  iTR 30 ISOTOPE PRODUCTION CYCLOTRONCHEMISTRYA N N E X42 MeV ISOTOPE P R O D U C TIO N  C Y C LO TR O Nk ( P )  / B L I B ( P )M E S O N  HALL EX TE N S IO NM E S O N  HALLM13(TT/jj), M i i ( r r )  dINTERIMRADIOISOTOPELABORATORYN EU TR O NA C TIV A TIO NANALYSISBAT H OBIOMEDICALLABORATORYTHERMALN EU TR O NFACILITYM E S O N  HALLSERVICEA N N E XJOURCERIZED>OURCEThis annual report is dedicated to the m em ory o f Professor John Bernard WarrenJohn Warren, who passed away suddenly on September 7, 1989, has been a dominant figure in the entire life o f  T R IU M F. He established the nuclear physics team at the University o f British Colum bia, from  which the T R IU M F idea emerged in the mid 1960’s. John becam e the first director o f  T R IU M F (1968-1971) and has played an im portant role in much o f T R IU M F ’s science, until the very last days o f his life.John was an outstanding teacher -  he personally supervised many dozens o f  Canadian grad­uate students over four and a half decades, and they constituted a large fraction o f  the early generations o f  Canadian nuclear physicists. He was a visionary scientist and engineer, with interests which encompassed much o f  science and technology. He contributed enormously to his chosen country, Canada, and especially to his province, British Colum bia, whose interests he pursued with singular passion. A bove all, John ’s youthful com pulsion for new science, evident in overnight experimental runs even during his final illness, was responsible for much o f  the best that has emerged from  T R IU M F. He was much loved and is greatly missed by everyone at T R IU M F .FOREWORDThe year 1989 was a very im portant one for T R I­UMF. Against the background o f  a highly successful and productive period o f  operation o f  the cyclotron, both the Federal-Provincial Project Definition Study (PD S) for the K A O N  Factory and the E bco cyclotron project moved on towards the prospect o f  their suc­cessful com pletions in 1990. In addition, the Board o f Management o f  T R IU M F  was impelled to re-examine the m ode o f  management o f  T R IU M F as a national fa­cility and the basic relationship o f  T R IU M F with the federal government.Despite the perturbations caused by the PDS and the E bco cyclotron and some extreme financial diffi­culties and uncertainties, the scientific output o f  the TR IU M F  cyclotron was superlative. A  record amount o f  beam tim e was recorded. This produced a crop o f im portant discoveries in three main areas: proton, pion and muon physics. It also perm itted the applied pro­gram to advance in areas including pion cancer therapy and positron emission tom ography (P E T ).The PDS moved ahead as planned under the capa­ble leadership o f  John Elliott. Alan Astbury directed the technical studies at T R IU M F  which are described in this report, as are a series o f  scientific workshops. These are expected to lead, in 1990, to a strong en­dorsement o f  the K A O N  Factory. An indicator o f  the potential for technology transfer at the K A O N  Factory is the 30 M eV cyclotron, whose construction was un­dertaken in 1989 by E bco at T R IU M F. This cyclotron (to  be successfully comm issioned in 1990) is used for the production o f  isotopes for medical, industrial and research applications.In addition to these exciting scientific and technical activities, the Board o f Management (and especially its chairman) found itself at the centre o f intense dis­cussions about the management o f  T R IU M F  and the fundamental nature o f  the relationship between T R I­UM F and the federal government. T R IU M F is a na­tional facility which is managed as the jo in t venture o f four western Canadian universities; recently, four more universities (including, in 1989, the University o f  Man­itoba) have jo ined  as associate members, so that now every province west o f  the maritimes is represented at the Board table. Management by the universities sat­isfies a number o f  national objectives, including the creation and dissemination o f  knowledge, the develop­ment o f  human resources through the em bedding o f  re­search in graduate training, and the efficient, effective transfer o f  technology. These advantages are inherent in the many activities described in this report. This m odel for the management o f  a national facility by a consortium  o f  universities is com m on in the United States, but is unique in Canada at T R IU M F . Under consideration is a m odification o f  the legal structure to establish T R IU M F  as a corporation whose mem­bers would be the T R IU M F  universities. In proposing incorporation, the Board has endorsed the consortium model o f  management.Operating funds for T R IU M F ’s basic research pro­gram, including the operation o f  the cyclotron, flow from  the federal government as a contribution, through the National Research Council (N R C ). Until 1989, the unquestioned role o f  the NRC was one o f  monitoring the use o f  that contribution to ensure responsible ac­countability for the federal contribution. N R C ’s A dvi­sory Board on T R IU M F  (A B O T ), under the very able chairmanship o f  Dr. Paul Redhead since its inception, was a very effective instrument for performing the nec­essary monitoring. Under this arm ’s length relationship with the federal government, T R IU M F  has prospered and Canada has benefitted.In 1989, changes in NRC administration led to a questioning in Ottawa o f  this long-standing, success­ful relationship. A t the same time, renewed difficulties were encountered with the level o f  funding provided through N RC. This situation resulted in a series o f urgent consultations, meetings and correspondences. T R IU M F  administration and the Board o f  Manage­ment attem pted to achieve effective, fruitful com m u­nication with N R C  administration and through this, resolution o f  the conceptual and financial difficulties. Regrettably, the difficulties were not resolved at the end o f  1989 and a background o f  uncertainty remains. It is hoped that progress toward satisfactory resolu­tion will be possible after the decision on the initiation o f  the K A O N  Factory project. It is a tribute to the dedication and com m itm ent o f  TR IU M F  staff and sci­entists in the face o f  these difficulties that 1989 was such a productive period.In 1989, the Board o f  Management was pleased to welcome new members Dean Colin Jones, replacing Vice-President George Ivany, and Dr. David Measday, replacing Dr. John Warren. The Board notes with sad­ness the death o f  Dr. Warren on Sept. 7, 1989 and dedicates this annual report to his memory.B.P. d a y m a nChairman, Board o f  ManagementT R IU M F  was established in 1968 as a laboratory operated and to be used jointly by the University o f A lberta, Simon Fraser University, the University o f  V ictoria  and the University o f  British Colum bia. The facility is also open to other Canadian aswell as foreign users.The experimental programme is based on a cyclotron capable o f  producing three simultaneous beam s o f  protons, two o f  which are individually variable in energy, from  180-520 M eV, and the third fixed at 70 M eV. The potential for high beam  currents -  100 n A  at 500 M eV to 300 /iA  at 400 M eV -  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 biom edical research facility which uses mesons in cancer research and treatment.T he 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.T he laboratory employs approximately 391 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 program m e is about625.VICONTENTSIN T R O D U C TIO N  ..................................................................................................................................................................  lSCIENCE DIVISION ............................................................................................................................................................  2Introduction ..........................................................................................................................................................................  2Particle Physics ....................................................................................................................................................  5Charge symm etry breaking in np  elastic scattering at 350 M eV .................................................................  5Radiative muon capture on hydrogen ...................................................................................................................... 6Measurement o f  the flavour-conserving hadronic weak interaction .............................................................  8Radiative decay o f  the A  resonance .......................................................................................................................... 9Study o f  rare K  d e c a y s ....................................................................................................................................................Measurement o f  A —► n y  ..............................................................................................................................................11Measurement o f  ir~p —* 7r°7r°n ....................................................................................................................................12Nuclear Physics and Chemistry ......................................................................................................................................... 13Resonant structure in C u (p ,7r+ ) X :  A possible dibaryon signal ..................................................................... 13Spin-transfer measurements in nd —► p p ...................................................................................................................13Single pion production in np scattering ................................................................................................................... 14Research and development studies with TISOL ................................................................................................... 15Polarization transfer in inelastic proton scattering from  160  .......................................................................... 16The ( n ,p ' )  and (p, n) reactions on 14N .....................................................................................................................19Search for density dependence in muon catalyzed fusion o f  the p + d  —>3He+ 7  reaction ..................... 20The 4H e,208P b (7r+ , w+ n ~ )  reaction at Tt + =  280 M eV .....................................................................................21Pion-proton bremsstrahlung .........................................................................................................................................21M uonic hydrogen in v a c u u m .........................................................................................................................................23pn  <->• 7r-pp(15 0) ................................................................................................................................................................24Stretched states excited in (n ,p ) reactions on 14C, 26M g and 30Si ...............................................................25Measurements o f  spin transfer coefficients in pd elastic scattering ................................................................2545S c (n ,p )45Ca and 45S c (n ,p )45T i: A  significant test o f  model calculations in the ( /p )  shell ............. 25Measurements o f  analysing powers in low-energy nd  scattering .................................................................... 26A  search for deeply bound pionic states in 208Pb using the (n ,p 7r_ ) reactionat T„ =  418 M eV ..............................................................................................................................................................27The 6L i(p - ,2 t)v^  reaction ...................................................................................................................................... 27Measurement o f  (t/ S q t  for 13C ...................................................................................................................... 28Spin excitations in the deformed nuclei 154Sm, 158Gd and 168Er .................................................................. 29Spin-m om entum  correlations o f  nucleons in polarized 3 He .............................................................................. 30A search for an excited pion-bound state o f  the nucleon via p (p ,X + + )n  .................................................. 31Quasifree radiative pion capture on 160  at 90, 125 and 160 M eV ................................................................ 32Analysing powers in the reaction pp —► d7r4 very near threshold ...................................................................34Gam m a-neutrino angular correlation in muon capture on 26Si ...................................................................... 34Search for a strangeness —2 dibaryon .......................................................................................................................35Polarization and weak decay o f  hypernuclei ...........................................................................................................36Research in Chem istry and Solid-State Physics ...........................................................................................................33M uonium -substituted free radicals .............................................................................................................................33Kinetic isotope effects in the reaction o f muonium with the halogens ........................................................ 38Muon and muonium states via rf spectroscopy .....................................................................................................39pS R  studies o f  sub- and supercritical fluids ...................................................................................................... 41M uSR studies o f  dioxygen and ethylene physisorbed on pure silica powder ............................................ 43Chem istry o f  pionic hydrogen ..................................................................................................................................... 44p + SR tests o f  mechanisms for high temperature superconductivity ............................................................ 44pS R  studies o f  (L a S r)C u 0 4, B a (P b B i)0 3 and (B a K )B i0 3 .............................................................................49M uonium  reactivity enhancements ............................................................................................................................ hiM uonium  studies on copolym erization in micelles ...............................................................................................52M uonium  reactions with 0 2, CO and NO in high pressure moderators .................................................... 54Kinetic isotope effects in the reaction o f  muonium with the hydrogen halides ........................................54Secondary electron emission in /i-foil interactions ...............................................................................................55The effect o f  conduction electrons on the diffusion o f  light in terstitia ls ......................................................56A tom ic Physics .........................................................................................................................................................................51)The polarization o f  optically pumped Kb vapour ................................................................................................ 59Theoretical P r o g r a m ...............................................................................................................................................................62Introduction ....................................................................................................................................................................... 62Nuclear structure ............................................................................................................................................................. 62Few-nucleon processes .....................................................................................................................................................63Meson physics .................. 64Electron scattering ...........................................................................................................................................................66Q C D  and quark models ................................................................................................................................................. 68Electroweak interactions ............................................................................................................................................... 68Other topics ....................................................................................................................................................................... 69C om puting Services ............................................................................................................................................................... 71Experimental Facilities ......................................................................................................................................................... 72Development o f a laser-pumped polarized 3He target ..........................................................................................72Development o f  high-pressure polarized 3He target cells .................................................................................. 73TISO L ...................................................................................................................................................................................75CH AO S .................................................................................................................................................................................75D etector facility .................................................................................................................................................................76D A S S /S A S P  .......................................................................................................................................................................76A PP L IE D  P R O G R A M S , T E C H N O L O G Y  k  A D M IN ISTR A TIO N  DIVISION ............................................78A pplied Program s ................................................................................................................................................................... 78Biom edical program  .........................................................................................................................................................7842 M eV cyclotron fa c i l i t y ...............................................................................................................................................79R adioisotope processing (N ordion) ............................................................................................................................ 81Positron emission tom ography (P E T ) ........................................................................................................................ 81Tom ograph design ............................................................................................................................................................82T R IM  and beam  line 2C ............................................................................................................................................... 82M icrostructures and electronics .................................................................................................................................. 83Technology and Site Services ............................................................................................................................................. 84Safety program  ..................................................................................................................................................................84Building program ............................................................................................................................................................. 85Design office ....................................................................................................................................................................... 86Machine shop .....................................................................................................................................................................86Planning ...............................................................................................................................................................................86C Y C L O T R O N  DIVISION ...................................................................................................................................................88Introduction ...............................................................................................................................................................................66Beam Production .....................................................................................................................................................................90Beam Development .................................................................................................................................................................94Beam dynamics ................................................................................................................................................................. 94Experimental work ...........................................................................................................................................................96Beam line diagnostics ..................................................................................................................................................... 96Radio-frequency Systems ..................................................................................................................................................... 99Ion Sources and Injection Systems ................................................................................................................................. 101Primary Beam Lines ............................................................................................................................................................102C ontrol System .......................................................................................................................................................................103Rem ote H a n d lin g ................................................................................. jQgOperational Services .........................................................................................New Projects .........................................................  lnQ .KA O N  F A C T O R Y  P R O JE C T  DEFINITION ST U D Y  ................................................................... 110Introduction .....................................................................................  ^Science W orkshops ................................................................................. ............Accelerator Design ..................................................................................................................  I l lLattice studies ......................................................................... ............Tracking studies ............................................................................................................................   ^Polarized beams ...........................................................................................................................  ^Single-particle instabilities .............................................................................................................  213Collective instabilities ............................................................................................................ ^ 4Beam loading ................................................................................................................................  114H~ injection ......................................................................................... ............Transfer lines ...........................................................................................In strum entation ...............................................................................................................................  120Magnet Development ............................................................................................................................  ^20Magnet Power Supplies .............................................................................................Kickers ...............................................................................................................................................   ^ 4Radio-frequency Systems ......................................................................................................................  ^ 5Beam Pipe and Vacuum ........................................................................................................................  228H_ Extraction from  the T R IU M F  Cyclotron ............................................................................................. 229Controls ...................................................................................................  ........Experimental Areas ...........................................................................................................................  ^ 2Targets ................................................................. ......................Shielding ........................................................................................................................................  J 3JSystems Integration .........................................................................................................................  134E LE CTR O N ICS A N D  C O M P U T IN G  DIVISION .......................................................................... 136Introduction ............................................................... ..........Electronics Services .....................................................................................................................  ^2gProject Team A ...............................................................................................................................  ^ 7Project Team B ............................................................................................................................   ^ 7Data Analysis Centre (D A C ) ......................................................................................................... 238C ON FEREN CES, W O R K SH O PS AN D M EETINGS ........................................................................................ 240O R G A N IZA TIO N  ............................................................................................................................................  143APPE N D ICE SA . Publications .................................................................B. Users Group ........................„  _  .  160C. Experiment Proposals ......................................................................................................... jg 4IXINTRODUCTIONGreat K A O N  hopes, extreme financial pressures and an extraordinary amount o f  cyclotron beam time are the essence o f  this 1989 Annual R eport.The Project Definition Study (P D S), under the very able stewardship o f  A lan Astbury, was very nearly com pleted by the end o f  the year. The work o f  the PDS was carried out under the aegis o f  a federal-provincial steering com m ittee and included a range o f  techni­cal studies as well as science workshops and interna­tional consultations. This annual report describes the progress in 1989 on the technical com ponents o f  the PDS as well as the ten science workshops for KAON , which were held around the globe during the course o f  the year. Beyond the technical studies and science described here, the PDS also included consultations abroad with C anada’s prospective foreign partners in the project. Much o f  the mom entum  for K AO N  is be­ing established by the scientists from  abroad interested in pursuing the science opportunities o f  K AO N .The ongoing scientific program o f  T R IU M F  went ahead strongly during the year, in spite o f  the diversion o f  so many o f  the experts in accelerators and experi­mental facilities to the K A O N  studies. Paradoxically, this diversion created a quantum jum p upwards in the amount o f  beam  delivered. In a normal year, T R IU M F has unpolarized (high intensity) prim ary proton beams for six months, polarized beam for three months and m ajor shutdowns for the remaining three months. The m ajor shutdowns are normally devoted to m ajor cy­clotron improvements or to the installation o f  m ajor experimental facilities. In 1989, the personnel for the work o f  the m ajor shutdowns were, largely, diverted to KAO N . There was less tam pering with the cyclotron and the m ajor shutdowns were much shorter (totalling only seven weeks). In addition, the cyclotron behaved and went through the year relatively trauma-free. The result o f  all this was an accumulated beam-delivery about 50% greater than in any preceding year. In a sense this is like going on a splurge and blowing one ’s savings. It cannot be repeated.The splurge o f  beam  delivery produced much new and good  science as recorded in this report. The new science illustrates the diversity o f  the T R IU M F  pro­gram and the im portance o f  new experimental facili­ties.For muons, the new superconducting muon channel, built with the help o f  Tokyo University, was used for the first time for a variety o f  muon capture studies. Also muonic deuterium in vacuum was observed. T R I­U M F ’s muon channels are in great demand.For pions, the fundam ental scattering processes (-kN  k  ■kN N ) remain interesting -  and puzzling -  at low energies. Considerable effort is being given to develop­ing proper detectors (T R IU M F ’s new project here is C H AO S) with large acceptance and good  enough res­olution to expand the domain o f  pion studies to more com plex processes.T R IU M F ’s proton beams also remain in great de­mand. W ith its variable energy, polarized and high quality beams and with T R IU M F ’s C H A R G E X  facil­ity, our proton hall has given rise to a lot o f  interesting new nuclear physics at medium  energies.The activity o f  T R IU M F  scientists at facilities abroad form s an im portant part o f  the whole TRIU M F program. We are “plugged in” to the world network o f  large facilities in particle physics, not only through the m any foreign scientists who work at TRIU M F, but also in our own activities at Brookhaven, CERN, etc. The Princeton-B rookhaven-TR IU M F search for I<+ —* tt+ vv had some main data-taking runs in 1989. This experiment is one o f  the very im portant tests o f the standard model.The T R IU M F  theory group has only four perma­nent staff members, but it augments its activities with many research associates and visitors. In 1989, the the­ory group initiated a very successful summer school in Nuclear Physics for graduate students. Theorists seem to blossom  in the summer, at least if  one judges from the flowering o f  activity in our theory corridor in the middle o f  each year.The T R IU M F applied program  includes many sci­ence activities ranging from  medicine to electronics. In spite o f  the fact that much o f  this science is not closely related to subatom ic physics, each o f  the ac­tivities is closely tied to T R IU M F ’s cyclotron or its research program. In 1989, pion therapy continued its patient accrual for clinical trials o f  brain tumours and set the stage for future trials on prostate cancer. Ra­dioisotope chemistry remains a very im portant aspect o f  T R IU M F ’s science, as does the development o f  new techniques for positron emission tom ography (P E T ).The technology transfer activities o f  T R IU M F, in 1989, centred on the E bco 30 M eV cyclotron. The NRC A dvisory Board on T R IU M F  (A B O T ) recognized tech­nology transfer as an im portant general goal o f  T R I­UMF.In summary, 1989 found T R IU M F  in a position o f readiness for a K AO N  decision next year, while the ongoing cyclotron activities moved ahead strongly.SCIENCE DIVISIONI N T R O D U C T I O N1989 will be remem bered by the T R IU M F  experi­menters as an exceptional year in terms o f  beam de­livery. T he cyclotron perform ed extremely well with a reliability o f  83% and an extended beam  production period due to reduction o f  the cyclotron shutdown peri­ods. A  record 508 m A  h o f  high-intensity beam  was pro­duced over 33 weeks while 12 weeks o f polarized beam  was delivered. This report will present some o f  the highlights o f  the 73 experiments which received beam  time in 1989. The report also demonstrates the breadth o f  the science being done at T R IU M F  -  from  particle physics to nuclear astrophysics, from  condensed matter to chemistry to radiochemistry, from  instrumentation to isotope production , to cancer therapy and so on. This makes the laboratory such a marvellous, stimu­lating environment for cross-field fertilization o f ideas.The particle physics section presents the different milestones achieved by experiments which are typically o f longer-term  duration due to their complexity. They deal with fundamental questions related to the stan­dard m odel o f  quarks and leptons. Here at our energies the experim ents are subject to the com plexities intro­duced by the strong interactions. One sees a m otivation centred around a few questions which are addressed via experiments perform ed here or at the most appropri­ate facility. In particular a shift o f  interest toward the kaon system is apparent already in this report, and several o f our teams are working at the AGS facility at Brookhaven in anticipation o f  our future K A O N  accel­erator.In the elementary purely hadronic system , the Man­itoba group is searching for evidence o f charge symme­try breaking and parity violation. Im portant progress was realised this year, and we hope to schedule the data-taking part o f  the former in 1990 while the latter experiment is in the middle o f  a two-year program o f development.We made considerable progress on the study o f a very fundamental elementary reaction, the radiative muon capture on hydrogen. T he new detector and the im proved beam  line were comm issioned this year, and we are looking forward to having the first ever mea­surement o f  this reaction next year.Another group, specialized in the detection o f  high- energy photons, has pursued the study o f elementary radiative processes in either the Tt~ p or the I\ p  sys­tems using T R IU M F  and A G S facilities.The Princeton-B rookhaven-TR IU M F group has continued their search for rare kaon decays at the AGSand reports here on the main data-taking run o f  1989 and the results from  the first run in 1988. This exper­iment represents a crucial test o f  the standard model and has attracted a lot o f  attention recently.W ith  the first year o f  operation o f  the superconduct­ing muon channel a increase o f  activity in the field o f muon capture has occurred. Experim ent 570 had a pre­liminary run to study gam m a-!/ angular correlations in 28Si to study possible renormalisation effects o f gp, the induced pseudoscalar coupling constant; Expt. 569 will study high-energy protons and deuterons following p~ capture in 3He, and a test o f  the 6L i(p  , reac­tion was conducted to assess the feasibility o f  using this reaction to measure the mass.Considerable excitement was generated by the ob ­servation o f  a large emission o f  neutral m uonic atoms from  capture o f  p~  in a solid hydrogen layer. Following intensive discussions during the summer, in particular with Soviet colleagues, one is now certain that it is not / i “ H but p ~ D  due to the traces o f  D present in nor­mal hydrogen. p~T> atom  form ation and diffusion in hydrogen layers is a subject o f  interest to the p. catal­ysed fusion community. As well, a source o f  slow p~  could be developed.Our pion beams are in very high demand. The pro­gram is dom inated by the study o f  few-nucleon systems and relies heavily on our polarized cryogenic targets. The success o f  the target group in producing high- polarization, reliable targets has only created more and more pressure from  the insatiable appetites o f our ex­perimenters.A  study o f  pion-proton bremsstrahlung took place with positive pions. Because o f  the sensitivity o f  the asymmetry to the magnetic mom ent o f  the delta reso­nance, the experiment was done on polarized protons from  the T R IU M F  frozen spin target.Several experiments by the 7r scattering group were aimed at the resolution o f inconsistencies between phase-shift predictions and data at low energies and between data sets. Also, measurements o f  analysing powers in low-energy nd scattering are in progress and will more or less com plete our exploration o f the itN  N  system at low energies. The next step will be to study the break-up channel.T w o experiments were devoted to  the search for deeply bound states o f  7r~, one via the n ,pn  reac­tion using the C H A R G E X  facility, the other through a 7r_ —► e~ v  decay search in ir~ atoms. The first ex­periment failed to see the large effects predicted by2the crude plane wave models and are more consistent with recent distorted wave estimates. Experiment 550 is studying pion photoproduction  amplitudes via the reverse process, pion radiative capture in nuclei.In the proton hall considerable effort is still spent on understanding the elementary process o f  tt produc­tion. An experiment explored the pp  —*■ d?r+ ampli­tude very near threshold, while Expt. 460 measured angular distributions and asymmetries for the reaction pn —► p p (}S o )n ~ . O f course, this is tying together the studies o f  7r+ d —► pp done by other groups at TR IU M F.The C H A R G E X  facility was again very much in de­mand (Expts. 538, 535, 470 ... ). The relationship be­tween weak m atrix elements and Gam ow-Teller transi­tions has been studied now in both p, n and n ,p  chan­nels, and these reactions were used to study stretched states in several nuclei.Our polarized proton beams are always oversub­scribed. Spin-transfer coefficients in pd elastic scatter­ing made use o f  our longitudinally and sideways po­larized beams. A  very new polarized 3He target was comm issioned after heroic efforts by the experimental team led by 0 .  Hausser and is opening up a broad range o f  experimental possibilities both with protons, pions and muons. This should be considered as an im­portant breakthrough which will result in an active program o f  science for the next several years. After H2 and more recently D 2, the next few years will see a pre­eminence o f  3He as the target o f  choice in the TR IU M F program.T w o new m ajor facilities are being developed for the nuclear physics program : A  second arm spectrom ­eter (SA SP) with large acceptance will be fitted at the target location o f  the Medium Resolution Spectrome­ter allowing high resolution coincidence experiments or low cross section measurements; The construction o f  a large angular acceptance spectrom eter for pion physics (C H A O S) was initiated in the Meson Hall with funding from  NSERC and foreign partners. These investments are essential to keep our user com m unity interested in our facilities.Also, in nuclear physics, the m om entum  o f  the K A O N  factory and its associated science workshops have been translated into action by several groups from  T R IU M F , who are now involved at KEK and BNL in hypernuclear physics and strange baryon searches.In another domain, the test facility for on-line iso­tope production, TISO L, was used to comm ission a new E C R  (electron cyclotron resonance) source which promises very high yields o f  radioactive isotopes. This new exciting development has already triggered several proposals, and again a window o f  opportunity now ex­ists to use these exotic nuclei, in particular for astro-physical reaction studies. This may lead to an eventual post-accelerator system to further increase the energy o f  these radioactive beams, a facility now becom ing the focus o f attention o f  numerous physicists worldwide.In chemistry and solid-state physics, every hour o f beam time is dearly fought for. T he study o f  high- temperature superconductors has for another year dominated the program  in condensed matter physics. Muons are ideal probes o f  the local magnetic fields in these structures. New varieties o f  com pounds keep ap­pearing, and the pS R  group has been very responsive to requests to test these new samples. This field is mov­ing very fast, and T R IU M F  has accepted the challenge o f  keeping pace by providing facilities and support for these activities. In parallel, studies o f  muonium diffu­sion are in progress which are related to some aspects o f  the studies o f  superconductors, but are also very interesting in their own right.Our chemists are also very active and use the light hydrogen-like muonium  atom  to study chemical rate effects. To use this probe effectively, the study o f  muo­nium form ation and muon polarization in fluids is es­sential. Having characterized the probe, one can then study, for example, free radicals and reactivity for the purpose o f  testing m odels with other isotopes o f  hy­drogen.The very diverse science which is accessible experi­mentally at T R IU M F  is also supported by a very dy­namic team o f  theorists, who have attracted a record number o f  visitors this year. T w o highlights are to be mentioned, the organization o f  a very successful confer­ence on few -body problem s (and related topical work­shops) which gathered more than 450 participants, and a new initiative which is centred around a Summer School in Nuclear Physics for graduate students. This initiative was very well received and should provide universities in Canada with an option  for a course in nuclear physics given by the best specialists in the world.The theory group reports here on their research, which is very much oriented to support the TRIU M F experimental program. A  close symbiosis is maintained with the experimenters, and here also the interest gen­erated by the physics o f  K A O N  has led to a significant participation o f  the group in the workshops which help define the science and form the initial experimental program.T R IU M F  is at a crossroads and has a bright future in view. The effort and unconditional support o f  the staff made this year a very productive one and is a guarantee that the faith that our future partners in K A O N  have expressed for our capabilities will not have been misguided.3The 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 of the authors.4P A R T I C L E  P H Y S I C SE xperim ent 369C harge sym m etry  break ing in np elastic scatteringat 350 M e V  (L .G . Greeniaus, Alberta; W .T .H  van Oers, Manitoba)An experiment similar in most respects to the com ­pleted T R IU M F  Expt. 121 is proposed to test for the isospin mixing com ponent o f  the neutron-proton inter­action at 350 M eV. The experim ent will measure the difference in analysing powers A p and A n (where the subscript denotes the polarized nucleon) at the zero- crossing angle. Designed as a null measurement, the experiment is to achieve an accuracy in A  A  =  A n—A p o f  ±0 .0005 (±0 .015° in the zero-crossing angle).Charge sym m etry leads to the com plete separation o f the isoscalar and isovector com ponents o f  the np 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 ) =  A p(9). A  nonvanishing asymmetry dif­ference is directly proportional to the isospin singlet- triplet mixing amplitude and therefore direct evidence o f  a CSB term in the interaction.A measurement [Abegg et al., Phys. Rev. Lett. 56, 2571 (1986)] o f  A  A  at the zero-crossing angle at an incident neutron energy o f  477 M eV has yielded A  A  =  (47 ± 2 2  ± 8) x 10- 4 . This result should be compared to the range o f  values from  the most recent theoretical calculations [Miller et al., Phys. Rev. Lett. 56, 2567(1986); W illiams 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. B 195, 121 (1987); Beyer and W illiams, Phys. Rev. C 38, 779 (1988); Niskanen, Sebestyen and Thom as, Phys. Rev. C 38, 838 (1988); Niskanen and Thom as, Aust. J. Phys. (to  be published); Iqbal and Niskanen, private comm unication] o f  (22 -74 ) x 10~4. These calcu­lations include (collectively) estimates o f  contributions from  direct EM effects, the neutron-proton mass dif­ference in one-pion and p-exchanges, and the isospin m ixing p-ui meson exchange. Some other smaller effects have also been evaluated. Beyer and W illiams op. cit. have found that the co-ordinate space Bonn potential does not agree with our 477 M eV result but other m od­els are in reasonable agreement. In Fig. 1 predications at 350 M eV by W illiams, Thom as and Miller (W T M ) [op. c it ] , Holzenkamp, Holinde and Thom as (H H T) [op. c i t ] ,  and Ge and Svenne (G S) [op. c it ]  are com ­pared. T he EM term accounts for much o f  the W T M - GS difference. The W T M -H H T  difference is due to the treatment o f  the p and p-ui terms. CSB experiments sensitive to the region away from  the zero-crossing an­gle can possibly distinguish these latter terms, but even measurements at the zero-crossing angle provide use­ful tests o f  the meson-exchange picture for the N  N  interaction at short distances.The 188 M eV experiment at IUCF [Vigdor et al., in Polarization Phenomena in Nuclear Physics -  1980, A IP C P # 6 9  (AIP, New York, 1981), p. 1455] has com ­pleted its data-taking and preliminary results have been presented [Jacobs, Proc., W orkshop on Spin and Symmetries, Vancouver, 1989, T R IU M F  report, T R I -  89-5]. It should lead to a result with a statistical accu­racy in A A  o f  ±0 .0013  in eight angle bins in the range 60°-120° c.m. Data centred around the zero-crossing angle (82 .4°-116 .1°) yield A A  =  ( 3 2 ± 6 ± 6 ) ±  1CT4. There are considerable differences in the theoretical predictions at this energy. This large result indicates the presence o f  significant contributions due to p-u  mixing. It is im portant to confirm the predictions with independent data o f  similar precision at a different energy. As a result we propose to improve our pro­posed measurement by doubling the amount o f data collected.The experiment will be perform ed using a 350 MeV neutron beam  on beam  line 4 A /2  at the 9° port. The neutron beam  is produced in the conventional manner using an L D 2 target. The energy, polarization and po­sition o f  the primary proton beam  will be monitored and controlled as in Expt. 121. The np elastic scatter­ing detection apparatus, shown in Fig. 2, consists o f large solid-angle telescopes to detect the neutrons and protons in coincidence. Neutrons are detected at 33.0°Fig. 1 . Comparison of the A A angular distribution from WTM, GS and HHT. The crossover angle and the range of the experiment are shown by the arrows.5Fig. 2. Schematic layout of the Expt. 369 apparatus.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 system atic 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, perm itting an angle region that is asymmetric about the zero-crossing angle to be observed. This will allow an attempt to measure A A  both  where the interesting p-u  term is relatively large and the total CSB effect is zero. Using this large angle range will allow system atic errors introduced by uncertainties in the beam  and target polarizations to be understood.A stable proton beam intensity >1 .5  pA  with a po­larization on the order o f 70% is required. Adequate current from  the source has been demonstrated and work is progressing to increase the polarization to the desired level. This is a top priority at T R IU M F. The beam  energy m onitor/polarim eter has now been m od­ified to operate at the higher currents and lower en­ergy. New boom s needed to support the proton detec­tion apparatus and new pT O F  counters have been con­structed. The A E  counters have also been modified to improve the tim ing inform ation that can be obtained. The frozen spin target (F S T ) has been modified. Most o f the other equipment is available from  the Expt. 121 and A nn (E xpt. 182) set-ups. A dditional neutron bars will be used, as shown in Fig. 2, to extend the de­tectable neutron angle range.E xperim ent 452R adiative m uon  captu re  on  h ydrogen(G . Azuelos, M ontreal; M. Hasinoff, UBC)This experiment aims to determine gp, the induced pseudoscalar coupling constant o f the hadronic weak interaction, by measuring the the branching ratio for radiative muon capture (R M C ) on hydrogen (p~  + p  —► n +  +  7 ). W hile this process has been measuredin com plex nuclei, it has not yet been observed for hydrogen, due to the very low expected rate (only about 6 x 10-8  o f the muons stopping in a liquid hy­drogen target will undergo R M C ). The measurement will be made using a large-volume drift chamber as a pair spectrometer to detect the photons from  R M C . A6BIN COUNTSPH O TO N  E N E R G Y  (M eV )Fig. 3. Photon energy spectrum from n~ stopping in liquid hydrogen.description o f  the experiment and the detector can be found in the 1988 Annual R eport, p. 11).This year was one o f  intense effort for the group, with the com plete detector system and refurbished beam  line being comm issioned and initial measurements o f R M C  using nuclear targets being made. In addition, the first studies with the hydrogen target were per­formed.In January the com plete detector system was mounted in the spectrom eter magnet and all the read­out and trigger electronics were tested with beam. A f­ter this run the drift chamber was removed from  the magnet and one bad wire was restrung. The drift cham­ber was reinstalled in the magnet in time for a second experimental run in April. By the last few days o f  the April run the refurbished rf separator in the M9 beam line was fully operational and a ‘ clean’ muon beam  be­came available. W ith the separator on, the contamina­tion in the beam  at the experimental target was mea­sured to be n/n =  5 x 10~4 and e/fi =  5 x 10~2. This level o f  pion contam ination, in com bination with the rejection o f  any photon events in prom pt coincidence with a beam  particle, will reduce the background from  radiative pion capture to a manageable level. How­ever, large random wire rates were observed in the drift chamber when the rf separator was operating, due to pickup o f  rf noise. After this run RC filters were added to the high voltage lines o f  the drift chamber which served to reduce the rf pickup to below the discrimina­tor thresholds. The individual wire efficiencies o f  the drift chamber were measured to be >98 .5%  at the op­erating voltages o f  5.0, 5.1, 5.2 and 5.3 kV on layers 1-4, respectively.By July a liquid hydrogen target with a Cu flask was available. This was filled with ordinary hydrogen,rather than the deuterium-depleted ‘protium ’ that will be required for the final data-taking. However, this LH2 test run enabled measurements o f  the efficiency and resolution o f  the detector for medium-energy photons using the radiative pion capture reaction 7r_ +  p  -+  7 -1- n and photons from  the decay o f  7r°s produced in the charge exchange reaction 7r“  -(- p —> n° +  n (see Fig. 3). A  typical reconstructed photon event is shown in Fig. 4. The trigger rate using a p~  beam  was also studied and found to be quite manageable. The im­position o f  cuts on the data using the SSP front-end m icroprocessor further reduced the trigger rate so that the dead-time becam e negligible ( < 5% ).During an experimental run in O ctober R M C  data were recorded on a series o f  nuclear targets: A l, Si, Ca, M o, Sn and Pb. This inform ation will be comple­mentary to R M C  data obtained earlier using the T R I­UMF T P C  (E xpt. 249, 1988 Annual Report, p. 5.) and should shed light on the possibility o f  a ^-dependent renormalization o f  gp within the nucleus. These data will constitute the Ph.D . thesis o f  A . Serna-Angel (V ir­ginia Polytechnic Institute).In December the fraction o f  incident muons that stop in the walls o f  the target flask was measured using a ‘dum m y’ target with scintillators at the location o f  tar­get walls. M uon stops in the target walls cause back­ground from  R M C  in the wall material. Only 0.3% o f the incident muons were found to stop in the target walls, in good agreement with M onte Carlo predictions, which would cause an acceptable level o f  background. This measurement was made at an incident muon m o­mentum o f  62.8 M eV /c  with a total incident flux o f  620 K /s  at 150 /iA  o f  primary proton beam. It was found that the muon flux could be increased by another 20%7by raising the muon m om entum  to 65 M eV /c ; how­ever, the fraction o f  stops in the target also increased somewhat.A lso in Decem ber two m ethods o f  increasing the photon acceptance o f  the detector were studied. The first was to lower the spectrom eter magnetic field from  2.7 kG to 2.4 kG. This would entail some loss o f photon energy resolution but a gain o f  about 78% in the accep­tance for 60 M eV photons. A  second technique was to loosen the trigger requirement that both  tracks o f  the e+ e~ pair reach the scintillators outside the drift cham­ber, and instead accept events where only one track o f the pair reached these counters. This 1-D trigger was found to substantially increase the trigger rate, and hence the dead-tim e (to  about 25% ). However, the ac­ceptance for 60 M eV photons was increased by about 75%. Various m ethods o f  reducing the dead-tim e are being investigated. Loosening the trigger and lowering the m agnetic field at the same time was found to in­crease the acceptance at 60 M eV by 150%. The effect these changes would have on the critical high-energy ‘ tail’ in the photon energy resolution is being studied with M onte Carlo, but it appears that the resolution would still be acceptable. It is likely that the final ex­periment will involve one or both o f these m odifica­tions.The construction o f  the final liquid hydrogen target, designed to have a A u flask has proved to be trou­blesome despite various different fabrication schemes. T he possibility o f  constructing a flask using A g is now being investigated and a final target is expected to be ready by May 1990. Final data-taking on R M C  on hy­drogen will begin in July. The precision expected for gp is about 10%.E xperim ent 497M easurem ent o f  the flavour con serv in g  hadronic weak in teraction(J. Birchall, S .A. Page, W .T .H . van Oers, Manitoba)1989 marks the second year o f  instrumentation de­velopment and prototyping for the parity violation ex­periment at T R IU M F . W hile much has been accom ­plished, it will be necessary to spend another year o f active testing at T R IU M F before the final experiment to measure the longitudinal analysing power A z in p-p scattering to an accuracy o f  ± 2 x 10-8  can be mounted. The philosophy o f  the group is to perform  the measure­ments in a staged approach. It should be possible to move relatively quickly to com plete the first stage o f measurements in transmission geometry, and the scat­tering detector will be added at a later stage. T o move rapidly toward data-taking in the transmission mode, certain m odifications need to be made to the existingbeam  line, and a liquid hydrogen target meeting the ge­ometrical and heat load constraints o f  the experiment must be constructed by T R IU M F . Development work is also necessary to install additional control features in the new optically pum ped ion source (O PP IS).To perform  the transmission m ode measurement, the beam current will be measured upstream and down­stream o f  a liquid hydrogen target with a pair o f  trans­verse field parallel plate ionization chambers (T R IC s) filled with hydrogen gas. During the past year test mea­surements have been perform ed with prototype TR IC s on loan from  Los Alam os National Laboratory that were used in the 800 M eV A z measurements. It has been possible to set upper limits for the intrinsic noise and nonlinearity o f  the T R IC s under present condi­tions, and to establish im portant design criteria for the final ionization chambers.An upper limit on the differential nonlinearity o f  the gas gain in the T R IC s was obtained by subtracting the signals from  two T R IC s, separated by 2 m  along the beam line, and m odulating the beam  intensity at a known frequency. A  lock-in amplifier was used to mea­sure the amount o f  m odulation in the T R IC  difference signal that was in phase with the m odulations in beam  current. It was found that subtracting two T R IC  sig­nals reduced com m on m ode intensity fluctuations by at least a factor o f  1000. This upper lim it was suffi­cient to rule out beam  intensity fluctuations as a cause for the large noise figures observed in beam  line 4A by at least a factor o f  5.Further tests were carried out com paring a 10 cm wide sense region in an upstream T R IC  to a 15 cm wide sense region in a downstream T R IC , to enhance the sensitivity to beam  halo. The noise in this mode o f operation was enhanced by two orders o f  magnitude over that found by com paring identical sense regions, lending support to the idea that the noise is arising from  wandering beam  halo.A multifoil secondary electron emission (SEM ) halo monitor was constructed to directly measure the beam  fraction outside set diameters A  typical “best” tune consistently found 4 -5 %  o f  the beam  outside 1.5 in. and 2 -4%  outside 2.5 in. when the beam  was centred on the halo m onitor. This amount o f  beam  halo is unac­ceptable for the parity violation measurements. Beam optics calculations indicate that it will not be possible to focus the beam through the bending magnet 4AB2 and the existing collim ator im mediately downstream without introducing halo from  roughly 2%  o f  the beam  striking the collimator. In an effort to  cure this prob­lem T R IU M F has assigned a site engineer to design a remote mechanism for retracting the collimator from the beam  line during parity runs.W ith the intention to run the initial phase o f  the ex-periment in transmission geometry, the length o f  the LH2 target has been reconsidered. The counting time can be reduced by a factor o f  3.3 if  the target length is doubled, making that possibility extremely attractive. Beam transport calculations have been undertaken to determine whether spills can be kept to an acceptable level downstream o f  the target if  its length is increased to 40 cm . Initial results are encouraging, provided that the beam pipe is changed to 8 in. diameter in this re­gion.Our program  o f  M onte Carlo simulations o f  the de­tector response to realistic beam  conditions has con­tinued during the past year, with encouraging results. It was found that a crossover occurs in the sign o f  the false asymm etry as a function o f  the small angle bound­ary o f  the detector acceptance between 5 and 6° (lab). The design o f  the final T R IC s is almost com pleted and it is planned that construction will begin in 1990.W ork has continued to optimize the elements o f the beam  position feedback system to the needs o f  the par­ity violation measurements. In the past year one o f the two hydrogen-filled split plate ionization chambers (SPICs) borrowed from  Los Alam os for prototyping and development work has been replaced by a split foil SEM device constructed at T R IU M F  which works in vacuum, reducing the amount o f  material in the beam  by roughly an order o f  magnitude. The signals from  the SEM device are much smaller than from  the SPIC, and necessitated the construction o f  new, sensi­tive electrometer-based preamplifiers with two orders o f magnitude higher gain than the original low noise preamplifiers used with the SPICs. In 1990 a second SEM monitor will be built at M anitoba to complete the system. Further development work will focus on optim izing the balance between the frequency response and the signal-to-noise ratio o f  these detectors.In development o f  a precision beam intensity pro­file m onitor, success was recently achieved at manu­facturing thin multi-strip foil arrays that approach the geometrical tolerances set by the system atic error cal­culations. A  31-channel electrometer preamp unit has been constructed and successfully tested together with a foil strip array. W ith an electronic bandwidth suf­ficient to permit a profile measurement once per sec­ond, the intrinsic noise per channel is 3 pA  rms. Work is continuing on an algorithm  for gain-matching to the required accuracy, and on im proving the foil strip man­ufacturing technique.As discussed in previous reports, the dominant sys­tem atic error in the parity violation measurements is expected to arise from  residual transverse polarization com ponents in the longitudinally polarized beam. It will be necessary to measure the profile o f  these polar­ization com ponents within the beam  envelope in orderto compensate for their effects in the final data. A  de­sign has been developed for a 4-branch “conventional” counting polarimeter with rotating blade targets, con­ceptually similar to polarimeters used in the PSI par­ity violation experiments. Final assembly drawings are now being prepared, following which construction will begin at the University o f  A lberta.E xperim ent 537R adiative decay  o f  the A  resonance(D .F . Measday, UBC)The study o f  the low-energy pion-nucleon interac­tion has intensified in the last few years because o f  the interest in the er-term and its calculation via the chiral perturbation theory o f  Q C D . Our earlier results from Expt. 9 are now published, viz. 7r~p  —► 771 [Bagheri et al., Phys. Rev. C 38, 875 (1988)] and tt~p  —  tt°n  [Bagheri et a l, Phys. Rev. C  38, 885 (1988)]. These measurements covered the energy range 45 <  Tw <  122 M eV  and the angular range 30 <  6  <  140°.This early experiment was limited by the energy res­olution o f  T IN A  (~ 5 %  at 150 M eV ), so proposals 257 and 258 were written to justify  a new detector. NSERC was unable to support this expensive device so the proposals rested in limbo until the Boston University crystal achieved a resolution o f  about 1.5%. W ith the prospect o f  this detector com ing to T R IU M F, a revised experiment (537) was proposed. The detector is ex­pected to travel from  Saskatoon in February or March o f  1990.In preparation for this experiment, some trial mea­surements were made on M i l  in December, using T IN A  set at 5°, using PA C M A N  to deflect the 7r~ beam. The forward angles are very im portant for both reactions. For 7r~p  —> n j  the multipole analyses dis­agree by a factor o f  2 at 0°. For n~p  -+  7r°n the en­ergy spectrum o f  the 7 -rays translates directly into an angular distribution o f  the 7r°. Unfortunately 0° itself was impossible because o f  bremsstrahlung from  the e~ com ponent o f  the beam, but at 5° the background was under control. A t one pion energy we also attempted a measurement with T IN A  at 170° where PACM AN  was placed upstream deflecting the pions before the hydro­gen target, so that sufficient space was obtained for setting up T IN A  at the far backward angle. Excellent data were obtained (see Fig. 5) and will be analysed by M. Halka o f  the University o f  New M exico and by A . Bagheri o f  Colum bia College, Vancouver.In the summer o f  1990 it is hoped that further ener­gies and angles can be studied, using the Boston Uni­versity crystal (or the Kentucky University crystal if Bicron produce a good ingot o f  N al).9Counts CountsFig. 5. Raw 7 -energy spectra measured at Tt =  79 MeV (~76 MeV at the centre of the target) for lab angles at 5° (top) and 170° (bottom). The background from the empty target is not subtracted yet.S tu dy  o f  rare K  decaysB N L  787 (B N L -P r in ce to n -T R IU M F  co llabora tion )(D. Bryman, TRIJJMF/Victoria)Certain rare decays which are forbidden to first or­der in the standard m odel (SM ) offer the possibility o f a sensitive and clean test o f  higher-order processes and m ay reveal the presence o f new effects that could suggest extensions to  the SM.Brookhaven Expt. 787 is sensitive to all processes o f the form  I<+ - *  t t+ A 0, where X °  is any light, weakly interacting neutral or system o f  neutrals. The reaction K +  _► tt+i/F is o f  particular interest, since it is a prime example o f  a flavour-changing neutral current process, forbidden to lowest order by the Glashow-Iliopoulos- Maiani (G IM ) mechanism, but allowed via higher- order weak diagrams, where mass differences between the internal quarks spoil the GIM  cancellation. The six-quark SM prediction for the branching ratio lies inthe range B (I< + ->• tt+i/F) ~  (1 -8 ) x 10 10, depending upon the top-quark mass and the Kobayashi-Maskawa m atrix elements.Beyond the SM, X °  might represent a pair o f  light supersymmetric particles or a pair o f  majorons. Single­particle possibilities for A °  include light Higgs parti­cles and G oldstone bosons, such as the fam ilon particle postulated as a by-product o f  the spontaneous break­down o f fam ily symmetry. The window for such exotic effects appearing unam biguously extends two orders o f magnitude from  the current limit B (I< + —* 7r+ A ° )  <1.4 x 10-7  to the upper level o f  the SM predicted range for K +  —*■ 7t+ i/F.This year data from  a two-week run in 1988, which followed the comm issioning and calibration o f  the de­tector, were analysed and results accepted for publica­tions [Atiya et al., Phys. Rev. Lett. 63 , 2177 (1989); ibid. 6 4  (in press)]. In 1989 a 10-week data-collecting run was com pleted in June.In the 1988 data, which corresponds to 1 .2 4 x l0 10 kaon stops, no candidate events were found in the ac­cessible kinematic region above the K t i peak which comprises approximately 17% o f  the available phase space for K + —* 7r+ vV. W ith  an overall acceptance o f  0.0055 we obtain a new limit on the branching ra­tio for K + -+  x+ i/F  (or I<+ - *  tt+ A 0) o f  B (I< + -► tc+ vF) <  3.4 x  10-8  (90%  C .L .). For the hypotheti­cal tw o-body decay K + —» 7r+ a the limit is B (A '+ —+ 7T+a) <  6.4 x 10-9  (90%  C .L .) where a represents any light, noninteracting particle such as an axion or familon.In addition to the primary search for processes like K +  t t+ X 0, the 1988 data set was used to extract more sensitive limits on other processes including de­cays involving light Higgs particles K + -+  7r+ / / ;  H  —► and direct (continuum ) decays K + —*-C+ F+ F-  and I<+ —* fi+ fi+ fi~Vp. Three candidate events o f  the type I<+ —*• n+ n + n~ were observed with expected background (due to particle m isidentification), 0.3T0.3 events from  I<+ —*• 7r+ 7r~e+ i/. Based on these data we can set limits for K + —► n+ H ] H  —► p + F f ° r HigSs particles in the mass range 220 <  run <  230 M e V /c2, as shown in Fig. 6 . Table I lists (prelim inary) limits for K + - *  n+ n + fi~ and I<+ -»■ We alsosearched for I<+ - »  n + j j  and K +  -+  tt+tt0; tt0 -♦  vv  and found no candidate events, leading to the results shown in Table I. The 1989 data should allow the sen­sitivity to be increased by a factor 5 to 10.The T R IU M F  group contributes extensively to the analysis o f Expt. 787 data. R econstruction routines for the drift chambers, beam  counters, range stack and endcap veto have been written by members o f  the T R I­UM F group. A  package o f  subroutines has been written which outputs the results o f  the reconstruction so that10Table I. Summary o f  results from  the Expt. 787 1988 run.ProcessBranching ratio limits (90%  C .L .)K + —* n+i'T/ < 3 .4  x 10-8K + —*■ x + a <6 .4  x lO -9K +  — tt+ H , H  —  p + p ~ a < 1 .5  x 10-7K + —+ TT+ p + p~ < 2 .3 x  10~7K + —► p + p~  p + u < 4 .1 x l0 ~ 7K + —* 7r+ 77 < 10-67r° _► 1/1/ < 8 x l 0-7a220 < m H <  3 20M eV /c2.it is not necessary to redo the reconstruction on subse­quent passes through the data. A  version o f  the analy­sis program  K O FIA  with all its reconstruction routines has been written for the A C P  m icroprocessor system for on-line use as well as for VAXes and, more recently, for the UNIX-based Decstation. Also, a custom  sys­tem for the management o f  all calibration constants has been written and has been used on both V A X  and A C P  systems.Full analyses o f  the K + —► 7r+ uv  data sets as well as the K + —*• 7r+ /r+ /z~ and K + —+ ir+ y y  data are under way at T R IU M F.The Expt. 787 collaboration intends to continue the search for the decay K + —► tt+ iSv  in order to cover the entire range o f  branching ratios predicted by the standard m odel with three generations. To accomplish this, we require sufficient I<+ flux and acceptance to reach a sensitivity o f  a few x  10~n /event. The upcom ­ing 15-week run in 1990 at m oderately higher K  fluxFig. 6 . The 90% confidence level upper limits of the branch­ing ratio for the decay K + —► H, H  -+ /r+ fi~ , as a function of r a j  (solid line). Also shown (dashed line) is the result of an inclusive search for K + —► x+ A °.will more than double the sensitivity possible with the existing data. Beyond that, substantial upgrades in the experiment will be necessary.The primary new feature required is a I<+ beam  line which can provide substantially more kaons but with reduced contamination from  other particles. A  design for the new beam line was developed at TR IU M F by J. Doornbos. This new beam  has approximately three times the K + flux (per incident proton) and 0.3 times the 7r, p  flux o f  LESBI. The order-of-magnitude im­provement in the purity o f  the new beam results from using two stages o f  separation. T he increased flux de­rives from  the placement o f  quadrupoles directly down­stream from  the production target.M easurem ent o f  A —+ n-f B N L  811 (B irm in gh am -B N L -B oston -C ase  W estern -N ew  M ex ico -P r in ce to n -T R IU M F -U B C  co llabora tion ) (D .F . Measday, UBC)The data-taking for this experiment was completed in May and all the measurements are now under anal­ysis.T he results on the first phase have now all been writ­ten up and most were published in 1989. The measure­ments included a new value from  the branching ratio o f  £ +  — p y  viz. (1 .4 5 ± 0 .2 0 ± 0 .1 1 )x  10~3, as well as branching ratios for kaon radiative capture in hydro­gen at rest, viz. K ~ p  —> A y , B R  =  (0.861q }3) x 10-3  and K ~ p  - *  E y, B R  =  (1 .44T0.23) x l ( T 3. The re­action K ~ d  —+ A n7 at rest was also observed for the first time and the branching ratio was measured to be K ~ d  - *  A n y , B R  =  (1 .9 4 ± 0 .1 2 ± 0 .2 0 )  x 10~3. R. W orkman and H. Fearing have discussed this reaction with a view to determining the An  scattering length. Unfortunately the experimental results lack the preci­sion and resolution to make a useful contribution to this topic.The next experiment was an attem pt to determine the branching ratio for the radiative decay A —> ny. Very few o f  these strangeness-changing radiative de­cays have been studied, and there is a significant con­troversy over how to interpret what few data are avail­able. A  recent preprint by P. Zenczykowski o f  Guelph University (G IP P -8 9 -2 ) has highlighted some o f the problems.To detect this decay a A is produced by stopping a I<~ in liquid hydrogen; the reaction K ~ p  —* A x° has a branching ratio o f  about 7% and the x° can be identified by its decay gam m a rays. The LA M PF  crys­tal box was successfully used as the detector although its 2x coverage was a difficulty. This device was also used to detect the high-energy 7 -ray which comes from the decay A —► n y. Background comes from  the much11Fig. 7. Doppler-corrected gamma-ray energy for the decay A _> The bump at 160 MeV is attributed to this weak radiative decay.more prolific decay A —► A 7t° as well as from  the in­flight reaction I<~p  —► K °n  —> 7r°7r°n. Events have been identified and the analysis is progressing well. The data from  the 1988 run will constitute the thesis o f A .J. Noble o f  UBC. A preliminary histogram from  that data set is presented in Fig. 7. The bump at a gam m a-ray energy o f  160 M eV is thought to be from  the decay A —► n y, although preliminary estimates o f the branching ratio come out to be significantly higherthan the only other measurement, which was obtained by the Geneva-Rutherford group at C ER N . Their re­sult was B R  =  (1 .02±0.33) x lO - 3 , but Zenczykowski also prefers a higher value (~ 3 .2 x l0 ~ 3).M easurem ent o f  ir~p —► x ° i °n B N L  857 (B irm in gh am -B N L -B oston -C ase  W estern -N ew  M e x ico -P r in ce to n -T R IU M F -U B C  co llabora tion ) (M . Sevior, UBC)Following the successful com pletion o f  Expt. 811 at Brookhaven, it was decided to devote the final month o f  the slow extracted beam  in May to obtaining data on the reaction n~p  —► 7r°7r°n. The goal was to study the 7r°7r° interaction near to threshold, thereby deter­mining the 7T7T scattering length with a view to testing calculations o f chiral perturbation theory for Q C D .The preliminary impressions o f  the analysis are very satisfying because the reaction is clearly identified and the results are reasonable. The total cross sections tend to be above the analysis o f  M anley [Phys. Rev. D 30, 536 (1984)], but in agreement with the earlier (adm it­tedly poor quality) results from  several Russian groups.Some o f  the calibration checks are being made at T R IU M F , but the full brunt o f the load is being shoul­dered by J. Lowe who has sentenced himself to one year’s hard labour in Albuquerque, New M exico (a sup­posed sabbatical leave from  Birmingham University).12N U C L E A R  P H Y S IC S  A N D  C H E M IS T R YE xperim ent 298R esonant stru ctu re  in C u(p, x+ )X : A  possib le  d ibaryon  signal(S. Yen, TR IU M F)A  sharp resonant structure was observed by Krasnov ei al. [Phys. Lett. 108B , 11 (1982)] and by Julien et al. [Phys. Lett. 142B , 340 (1984); Saclay Note CEA - N-2483 (1986)], at a bom barding energy o f  350 M eV, in the inclusive yield o f  low-energy pions at 90°. The width o f  the resonance was less than 10 M eV. Julien et al. suggested that the resonance was due to the form a­tion o f  the 3f<3 dibaryon resonance at rest in the target nucleus, which subsequently decayed into a pion plus nucleon.The previous results used scintillator telescopes as the pion detectors. Since there are on the order o f  103 charged particles entering the scintillator array for ev­ery pion, we felt that a much cleaner trigger could be provided by a magnetic spectrom eter, such as the MRS spectrom eter in the T R IU M F  proton hall. Despite the long flight path o f  11 m, and the subsequently low sur­vival fraction o f  only 15% for 40 M eV pions, we were able to reject the decay muons by a com bination o f cuts on m om entum , time o f  flight, raytracing back to the target, and correlation o f  angles before and after the spectrom eter.Our first run in June was terminated by a faulty C A - M A C  branch coupler. A  second run, in O ctober, used a novel technique in which a copper target o f  thickness corresponding to 26 M eV energy loss was placed in the primary proton beam  o f  energy 363 MeV. In order to increase the spatial extent o f  the energy loss, slots o f  width 0.8 m m  were cut into the copper target ev­ery 1.6 mm , to form  a comb-like structure. The proton beam  was degraded in energy as it passed through the teeth o f  the com b, reaching the reported resonance en­ergy o f  350 M eV at the exact centre o f  the target. The excellent raytracing capabilities o f  the M RS enabled us to reconstruct the target position o f  each event. A plot o f  pion yield versus target position then gives a plot o f  yield versus bom barding energy. To account for sys­tem atic effects, such as a possible dependence o f spec­trometer acceptance as a function o f position, we took data for 40 M eV pions, which are reputed to resonate, and for 100 M eV pions, which are not supposed to res­onate. The ratio is shown in Fig. 8 . Some remnants o f  a periodic structure due to the teeth o f  the copper com b can be seen, due to im perfect correction for the different multiple scatterings o f  40 and 100 M eV pions. No resonant structure is seen; we can rule out a 50% enhancement, such as that reported by Krasnov et al. and probably the 10% effect reported by Julien et al.in 1984, but not the 5% effect reported by Julien et al. in 1986.A third run, in November, used a thin copper target and searched for a resonance by stepping the incident beam energy in 1 M eV steps from  360 to 340 MeV. A t each energy data were taken for 40 and 100 MeV pions and 250 M eV protons. We carefully searched for possible sources o f  system atic errors. T he secondary emission m onitor used to m onitor beam  flux was found to be spatially non-uniform  in its response, and the spatial acceptance o f  the spectrom eter was found to be different for the types/energies o f  particles measured. Calibration data were taken to correct for these effects. The data are under analysis.E xperim ent 331Spin-transfer m easurem ents in wd —► pp (A . Feltham, UBC)Experiment 331 was designed to obtain spin-transfer parameters o f  the fundamental pp  —> dir reaction over energies spanning the s-wave TV-A resonance (7>  =  500 to 800 M eV ). Such observables are required to remove ambiguities from  the partial wave amplitude (P W A ) analysis o f  the existing data at these energies. Our unique approach o f  measuring the time reversed 7rd —+ pp reaction provides several experimental advan­tages [Feltham et al., Contributed papers, Few Body XII, Vancouver (1989), E l l ] ,  Since there are different systematics, this experiment also acts as a consistency check for data obtained from  the pp  —+ dn direction.The data were obtained during 12 weeks o f beam time in 1987 and 1988 [1987, 1988 Annual Reports]. Progress in the past year has consisted o f a first-Y Ifl/ 1 0Fig. 8 . Ratio of yield of 40 MeV to 100 MeV pions, as a function o f horizontal position in the target. The error bars are statistical only.13order analysis o f  the spin-transfer parameters K l s , K s s , and K n n  using a large software base which has been created for this purpose.To date, preliminary results for K l s  and K s s  have been com pleted. These results are in qualitative agree­ment with prevalent PW A  fits [Bugg, Nucl. Phys., A 4 7 7 , 546 (1988)], which have been partially con­strained using theoretical input. Significant effort has been made to understand the systematic effects inher­ent in our proton polarimeter. Specifically, computer programs have been developed to model the spin pre­cession o f  the final-state protons in the magnetic field o f  the target. As well, we have estimated contributions to the polarization due to background processes and potential instrumental inefficiencies.U pon com pletion o f  our preliminary analysis, we in­tend to investigate the influence o f our data on the existing set o f  PW As mentioned above. It is our goal to obtain PW As which are independent o f  theoretical bias.E xperim ent 372Single p ion  p rod u ction  in np scattering (N. Davison, Manitoba)Recent experim ental investigations o f  the N N -N N n  reactions have been centred around the need to provide a broad data base and to investigate why the agree­ment between theory and experiment is poorer than expected. A lthough a phase-shift analysis is now possi­ble for both the pp ^  dn+ and pp —*■ pmr+ reactions, a m icroscopic description remains elusive. Typically, the general trend o f  the data can be reproduced, but with some notable exceptions such as the differential cross sections, the discrepancy between theory and experi­ment remains surprisingly large. It has been pointed out recently by Dubach et al. [Nucl. Phys. A 4 6 6 , 573 (1987) that the np - *  ppir-  reaction is one o f the most useful reactions to study in order to resolve remain­ing discrepancies in the N N -N N n  system. This work also suggests that the isospin 1 = 0  amplitudes (which do not involve the A  resonance at all) are as im por­tant in determining some spin observables as are the A -dom inated 7=1  amplitudes.Experiment 372 is designed to measure <r, A xo, A y 0  and A z 0  for np —> ppir~ in a kinematically complete experiment at an incident neutron energy o f 450 MeV. Experiment 372 is currently on the floor at T R IU M F and scheduled for final experimental runs in 1990.The detection apparatus consists o f  a time-of-flight (T O F ) start scintillator and a segmented T O F  stop scintillator consisting o f  18 bars o f bicron-408 each 200x 3 x 10.2 cm 3, and each viewed from  each end by a photomultiplier. T w o drift chambers, each with 6detection planes, lie between the T O F  start and the T O F  stop scintillators to determine the trajectories o f the two protons plus that o f  the pion if it also enters the forward cone. A dditional detectors assist in align­ment and m onitoring o f  the apparatus. The neutron beam polarization is determined using two neutron po­larization m onitors which measure the ratio o f  the X  and Y  com ponents o f  the polarization, one upstream o f  the neutron spin precession dipoles and one down­stream o f  the target. In addition, the absolute X  and Y  polarizations o f  the proton beam  are determined up­stream o f  the LD 2 neutron production target. W ith this (overconstrained) inform ation, it is possible to de­duce all three polarization com ponents o f  the neutron beam. Low-energy tails in the incident neutron beam  are removed during off-line analysis using the time dif­ference between the event trigger and the cyclotron rf phase locked to the proton beam  burst. In order to obtain sufficient resolution to reduce or eliminate the low-energy neutron tails, the proton beam  burst must last less than 0.5 ns. This requires a beam  that is phase restricted within the cyclotron. The cyclotron VAX730 computer is used to collect data on the width and dis­tribution o f  the proton burst and to send information to the M RS data acquisition com puter.During the last quarter o f  1989 all parts o f  the ap­paratus were brought on line and tested satisfactorily using unpolarized beam . In addition the proton spin precession solenoid on the 4B line and both neutron spin precession dipoles were calibrated.W ork has also proceeded on development o f  analy­sis programs using both M onte Carlo simulation and data from  the test run in July 1988 as well as runs in November and December 1989. Considerable effort has been expanded to develop reliable and redundant calibration procedures so that m ost crucial quantities (e.g. time-of-flight calibrations) can be determined in more than one way. W ork with M onte Carlo simula­tion events has led to the development o f  routines to identify tracks in the drift cham ber. The simulation in­cludes finite target size, multiple scattering and energy loss straggling, pion decay and some drift chamber fail­ure modes. Use o f real data has led to identification o f further “failure” modes and to algorithms for circum­venting them.It now appears that Expt. 372 will be able to run with a considerable degree o f  m onitoring in the acqui­sition com puter plus the full analysis program running on the T R IU M F com puter cluster and receiving data over Ethernet as time available on the cluster permits. The goal o f  having a detailed analysis o f  several per cent o f the data available during the experiment thus appears achievable.14E xperim ent 421R esearch  and d evelopm en t studies w ith  TISOL(J. D ’Auria, SFU)A t the end o f  1988 the main com ponents o f  the T I­SOL facility in the heated surface (or thermal) ion source configuration were com pleted, and Fig. 31 o f  last year’s Annual R eport displays an elevation view o f  the system at that time. Further details o f  this system can be found elsewhere [Oxorn et a l,  Nucl. Instrum. Meth­ods B 26 , 143 (1987); D ’Auria et al., Nucl. Intrum. M ethods B 4 0 /4 1 , 418 (1989)]. During the spring o f this year a series o f  runs were conducted to measure the production yield o f  all radioisotopes extracted from  a variety o f  target materials. To summarize, over 95 isotopes were measured from  the elements Li, Na, Al, K, Ga, R b, Sr, In, Cs, Y b  and Fr. Targets used with the thermal source ranged from  powders o f  SiC, ZrC, U O /C  and ScC, to foils o f  Zr, Nb, Ta and Ti. The ob­served yields are presented elsewhere [Dombsky et a l, to be subm itted to Nucl. Instrum. M ethods]. Some o f the highlights o f  this phase are the observation o f  ac­tivities as short as 20.3 ms for 24mNa, the observation o f  isotopes very close to the limits o f  present knowl­edge, such as 131In, 75R B, " R b  and 146Cs, and the relatively short half-lives.During the summer a significant change was made in the front-end o f  the TISO L facility. The electron cy­clotron resonance (E CS) ion source which had been de­signed here, constructed over the previous 12 months, and tested successfully in an off-line m ode, was in­stalled on-line at the front-end o f  TISOL.Figure 9 shows a similar configuration as Fig. 31 o f last year’s Annual Report, only now with the newly in­stalled and operational E C R  ion source in place, along with other m odifications to the pum ping system and ion transport system. The E C R  system consists o f  a small water-cooled target vacuum chamber in which is located the resistance-heated TA oven and a graphite chamber containing the target material itself. A  gas transfer line, connected both to an external gas sys­tem and the inlet o f  the E C R  source, is also connected to a small opening at the upper part o f  the oven/target chamber. Nuclear reaction products resulting from  the interaction o f  the proton beam with the heated target material can diffuse into this opening, but the trans­fer line is not heated at present so that only gaseous species are expected to reach the ion source. Ions pro­duced in the source are extracted out through a 2 mm hole using a specially shaped extraction electrode (EE) with a 3 m m  opening. As before, the accelerating po­tential at which the target operates is 20 kV. The re­mainder o f  the system is as before except for the use o f new (longer bore) magnetic quadrupoles and a mag­netic steerer, prior to the dipole.Figure 10 presents a detailed side view o f  the ECR source itself with the target chamber at its front end. In general rf waves o f  10 GHz at an injected power level o f  160 W  are used to provide the power to ionize the gaseous material which reaches the plasm a chamber o f the source. The electrons inside the plasm a spiral with their cyclotron frequence and are contained within the magnetic mirror coils o f  the source. Full details o f  this new source are presented elsewhere [Buchmann et a l, Nucl. Instrum. M ethods B 26 , 253 (1987); McNeely et a l, Int. Conf. on Ion Sources, Berkeley (in press); M c­Neely et a l, J. de Phys. 50, C l-8 0 7  (1989)].The E C R  ion source was used successfully with T I­SOL leading to the ionization and extraction o f  ra­dioisotopic beams o f  Ne, Ar and Cl. This is the first instance o f  the coupling o f  an ISOL device with such a source. Using a T i foil target heated up to about 1500°C, ion beams o f  Ne, Ar and Cl (as C l+ and HC1+) were observed. A n extraction potential o f  12 kV was used and in this first run a He carrier gas was used although the pressure in the target chamber was only o f  the order o f  10-5  torr. In a series o f  subsequent runs targets o f  M gO , CaO and U O /C  have been used and ion beams for isotopes from  nine elements (in differentFig. 9. A schematic representation of the elevation view of the TISOL facility, located on beam line 4A. The front end of TISOL shows the configuration for a new ECR ion source. In this configuration the target chamber is sepa- rated from the ion source.DetectionSystemsQuadrupoles, > Steerer —io And> t Deflector JawsMagneticSteererMagneticQuadsIonizer~T'" Magnetic *o DipoleTarge't15Fig. 10. A schematic, detailed representation of the newly installed ECR system at TISOL. The ion source is the large chamber on the left while the target chamber is on the right.chemical form ) have been observed. Further details o f these measurements can be found elsewhere [Dombsky, op. c i t ] .  T ypical target thicknesses used were in the range o f  1-10 g /c m 2 while proton beam  currents o f 200-300 nA were utilized.In summary, TISO L is now ready to initiate physics projects and the intention is that Expt. 421 be devoted to developing target systems leading to the ion beam  yields o f the particular radioisotopes needed to perform these projects. Three new experiment proposals (587, 589, 597) were presented to the winter meeting o f  the EEC.E xperim ent 432P olarization  transfer in inelastic p ro ton  scattering from  16 O(B. Larson, SFU; 0 . Hdusser, SFU /TRIU M F;D. Frekers, TRIU M F; R. Jeppesen, L A M P F )The aim o f  Expt. 432 is to test the effective proton- nucleus interaction at intermediate energies. This is ac­complished by measuring cross sections and a complete set o f spin observables for the reaction 160 (p, p') lead­ing to the ‘stretched’ 4“  states at excitation energies o f 17.79 M eV, 19.80 M eV (mainly T  =  0) and 18.98 MeV(!T  =  1) [Lindgren and Petrovich, in Spin Excita­tions in Nuclei (Plenum , N .Y ., 1984) p. 323; Holtcamp et al., Phys. Rev. Lett. 4 5 , 420 (1980)]. The isovec­tor interaction is dom inated by the tensor com ponent alone whereas the isoscalar interaction has contribu­tions from  both  the tensor and spin-orbit components. The state at u> =  18.98 M eV ( T = l )  is an excellent probe for the tensor piece o f  the isovector interaction. The other two 4“  states (m ostly T = 0 )  probe the rel­ative im portance o f  the tensor and spin-orbit pieces o f the isoscalar interaction. As a by-product, we obtain accurate inform ation about the ^-dependence o f spin observables for background continuum  states between u  =  17 and 22 M eV. These data are o f  interest for testing current m odels o f  quasielastic scattering.The experiment was carried out using polarized pro­ton beams in BL4B. Protons scattered off a waterfall target developed at Univ. o f  Toronto were mom en­tum  analysed with the m edium  resolution spectrom e­ter (M R S). The transverse spin com ponents o f  the pro­tons were determined by secondary inclusive scattering from  carbon using the M RS focal-plane polarimeter (F P P ). Prior to this year a total o f  16 shifts o f po­larized beam  time were consumed to determine cross sections, analysing powers, induced polarization and16' 0 (p,Pr o *----------------------SP84---------------------- GPHT =350  MeVp1.00.60.2- 0.2- 0.6- 1.0u = 18.98 MeV mainly T=110 20 30 40 50c.m.30 40(deg.)Fig. 1 1 . Angular distributions of D ,si , D sl/ and P  for the T =  1 state in 16 O . The meaning of the curves is given in the text.spin transfer coefficients D,,*  and D ,v at 350 MeV. The analysis o f  these data is com plete and a further 22 shifts o f  polarized beam  were used in July o f  this year to measure the remaining spin observables D nn, D lv and .D/,/, thus com pleting the set.The most striking feature o f  our previous data is a shift o f  the zero crossing o f  for the iso vector state com pared to theoretical calculation using the effective interaction o f  Franey and Love [Phys. Rev. C  31, 488 (1985)] and the density-dependent G -m atrix interac­tion o f  Rikus and von Geramb [Nucl. Phys. A 4 2 6 , 496 (1984)] (Fig. 11). In the plane-wave impulse ap­proxim ation the zero crossing is predicted to occur at a mom entum  transfer where the longitudinal and transverse pieces o f  the isovector tensor interaction are equal. Since V 1 and V * are both mixtures o f the central and tensor pieces o f  the effective interaction, this may be an indication that some retuning o f  the isovector interaction is required.The 4~ transitions occur in the energy loss re­gion o f  18 to 20 M eV, which samples the tail o f  the quasielastic peak. The data therefore complement ex­isting data sets at 500 M eV [Carey et al., Phys. Rev. Lett. 53, 144 (1984)] and 290 M eV [O. Hausser et al., Phys. Rev. Lett. 61, 822 (1988)]. Much theoret­ical work on quasielastic scattering has been done in the past few years with respect to reaction models and nuclear structure modifications. A t large momentum transfers shell effects are thought to be unimportant and a simpler m odel is supposed to describe the nu­clear surface adequately.We have available for comparison a calculation based on the semi-infinite slab model o f  Bertsch, Scholten and Esbensen [Bertsch and Scholten, Phys. Rev. C 25, 804 (1982); Esbensen and Bertsch, Ann. Phys. 157, 255 (1984), Phys. Rev. C 34, 1419 (1986)]. This model is based on the surface response o f  a semi-infinite slab o f  nuclear matter. The slab m odel cross section is given byd?adQdui (? .w ) ,where Nef[ is the effective number o f  nucleons partic­ipating in single collisions, <7/v./v is the free N N  cross section [Arndt et al., Phys. Rev. D 28, 97 (1983)], and St ,s is the surface nuclear response function. The sub­script T, (S )  refers to a specific isospin (spin) chan­nel. The contribution to the cross section from single and double scattering has been determined within the framework o f  Glauber theory [Bertsch and Scholten, op cit.; Smith and W ambach, Phys. Rev. C  36, 2704(1987)]. The effect o f  the residual interaction on the surface nucleons, treated in the RPA, has recently been incorporated into the model [Esbensen and Bertsch, op cit.]. The inclusion o f  (2p -2h ) excitations may also be im portant. These effects are expected to have a signifi­cant im pact on spin transfer. Data on spin observables are extremely rare and are o f  considerable interest in determining the magnitudes o f  such effects.We have measured the cross sections (d 2 a / dSldu), analysing powers, and the polarization transfer observ­ables P , D si' and D sp for inclusive proton scattering from  160  at 350 M eV incident proton energy. Our data cover an energy loss range o f  12 to 24 M eV at the lab­oratory angles 17°, 22°, 27° and 32°. We have also measured D w , D u > , and D nn at 17°, 22° and 27° but analysis o f these data is just beginning. It should be noted that the observables are strongly influenced by the existence o f  discrete states (including the 4 ~ states) below an excitation energy o f  about 20 MeV. The 20 to 24 M eV region is covered by broad over­lapping states and hence better represents an average quasielastic nuclear response. The jum p in the size o f17d2a/dfidw (mb/sr/MeV)160(p,p‘) " o '  T p =  350 MeVSRPA (la b ) __ __ __ Free (la b )1 7 °•r---- * _  — 4-:'“=- —"  • • •• .  * ’2 14 16 18 20 22 2422.5 °• J  „ * ___,----------- --!--- — -• —1 •1612 14 16 18 20 22 2412 14 18 18 20 22 24CO (MeV)Fig. 12. Energy distribution of cross sections for the four angles measured. The energy bins are 1 MeV wide and the points represent the total spectrum counts (peaks +  back­ground).the error bars at u) = ~  16MeV is due to the fact that the data below  this level were prescaled by a factor o f ten during data-taking in order to increase the per­centage o f 4 “  data written to tape.The cross sections (shown in Fig. 12) are well re­produced over more than an order o f  magnitude by either the free scattering calculation (dashed line) or the RPA calculation (solid line). The data only deviate from  the calculation at the largest angle. The analysing power data are presented in Fig. 13. They seem to be best represented by free (single particle) scattering. It should be noted that the residual interaction is not well known at this large m om entum  transfer and an al­ternative residual interaction has been suggested [R.S. Smith, private com m unication] which includes tt and p meson exchanges. This interaction is not presently included in the slab m odel code.l.o0.60.2- 0.2- 0.6- 1.00.60.2- 0.2- 0.6- 1.00.60.2- 0.2- 0.6- 1.00.60 2- 0.2- 0.6- 1.00(p,p')160* Tp = 350 MeV----------- ,------- ----I-----------1----------- 1-------- 1•--------------  SRPA (lab)------------- Free (lab) 17°.  r  * * • ,  • • • • 922.5°• • • • •27.5°’ 1 • ■ • ••• •- ----_i------------1----- —---- 1• •• •35°12 14 16 18 20 22 24CO (MeV)Fig. 13. Energy distribution of the analysing power for the four angles measured.T he m ost interesting aspect o f  the D aa< and data (Figs. 14 and 15) is the lack o f  an angle depen­dence contrary to the calculations. It is also interest­ing to note that the data seem to be best reproduced at the largest angle while the theory is thought to be m ost accurate at small angles [Esbensen and Bertsch, op. cit.].1816 0(p,p')160* T = 350 MeV0.2«  -° -2 CQQ  "° -6 - 1.00.60.2- 0.2- 0.6- 1.00.60.2- 0.2- 0.6- 1.0,w>#4---------J• ••— I 1 "|• • • r.SRPA (lab) Free (lab)■17°‘ ’•• • # • • •22°■ I * * * . #•• • •27°-  4 - . -  4 - •-  — -■ — — _ _ •; l i 1— I______•--1------------1______32°—1------------1--12 14 16 18 20 22 24CO (MeV)Fig. 14. Energy distribution of D ssi for the four angles mea­sured.E xperim ent 439T h e  (n,p ), (p,p ') and {p, n) reactions on  14N (K .P . Jackson, T R IU M F; A . Celler, W estern Ontario; A .I. Yavin, Tel-Aviv/TRIU M F)The data have been recorded in this study o f  charge exchange and inelastic scattering at 280 M eV and small mom entum  transfer on the self-conjugate target 14N. The primary objectives o f  this experiment involve de­tailed measurements o f  the distributions o f  Gam ow- Teller strength and a search for evidence o f  substantial breaking o f  isospin symmetry.The 14N (n ,p )14C data were recorded with nitro­gen gas at 20 atm in each o f  two cells 4.0 cm  long in the (n ,p )  gas target. The neutrons were produced with a dispersed primary proton beam  incident on a 90 m g /cm 2 strip o f  7Li, and on-line analyses indicated an overall resolution o f  < 1 .0  M eV. Data were recordedwith the M RS at 0°, 6°, 12° and 18°. To facilitate the normalization o f  the cross sections, data were also recorded with methane (C H 4) in the gas cells and as usual all data were recorded simultaneously with an160 (p ,p ')160* T = 350 MeV1 .0   —   p0.60.2 - 0.2 - 0.6 - 1.0 0.6 0.2 - 0.2 - 0.6 j J - 1.0 ^ 0.6 0.2 - 0.2 - 0.6 - 1.0 0.6 0.2 - 0.2 - 0.6 - 1.0-------------  SRPA ( la b )-  — — — Free (lab)17°II2 2 °h - f -27°± t32°t n - i -----------1CO (M eV )Fig. 15. Energy distribution of D,ii for the four angles mea­sured.(n ,p ) spectrum  originating in a solid C H 2 target.The 14N (p ,p ')14N reaction was studied with a melamine (C 6H12N12) target o f  11.3 m g /cm 2 evapo­rated on a 1.8 m g /cm 2 kapton foil. The M RS was used with dispersion m atching in the small angle configura­tion. Data were recorded with central angles o f  3.2°, 4.2°, 6.0°, 9.0° and 12.0°. On-line analyses indicated a resolution o f  <130 keV (F W H M ). Background mea­surements were made with both kapton and C H 2.The target for the study o f  the 14N(p, n )140  reaction was also melamine, in this case powder contained in a cell form ed from  a thin stainless steel foil. Neutron de­tection with a resolution o f  1.0 M eV was achieved using the MRS and the H (n ,p )  reaction in a liquid scintil­lator (C H 2). Background and norm alization measure­ments were recorded using primary targets o f  stainless steel and CH 2. In the limited time available data were recorded only at # m r s  =  0°.The prim ary goal o f  this experiment is an investiga­tion o f  the G T  strengths in a pair o f  2+ T = 1  states lo­cated at 7.01 and 8.32 M eV in 14C, 9.17 and 10.43 MeV in 14N and 6.59 and 7.77 M eV in 140 .  Shell model cal-19culations suggest that these doublets are formed by the strong mixing o f  one Ohu> ( I s 4 lp 10) and one 2hu  ( I s 4 lp 8 2s — Id 2) state. As predicted in the experi­mental proposal, these doublets dominate the spectra recorded at the m ost forward angles. If isospin were an exact sym m etry one expectsda . . da . . „ da .5 j j ( » , r t  =  5 S (P .» )  =  2 S (l>.I>)for each o f  the T - 1 states in 14C, 140  and 14N. As is outlined in the proposal, there is a reasonable expecta­tion that the three 2+ T =  1 doublets will exhibit a large isospin violation. Analysis o f  the data is in progress.E xperim ent 440Search fo r  density  d ep en d en ce  in m uon  cata lyzed  fusion  o f  the p +  d —►3H e+ T  reaction  (K . Aniol, California State L A )Recent measurements [Aniol et al., M uon Cat­alyzed Fusion W orkshop, A IP C P # 1 8 1  (AIP, New York, 1989), p. 68] o f  muon catalyzed fusion in gaseous mixtures o f  H2 and D 2 disagree with results obtained in liquid hydrogen. The source o f the discrepancy is not certain since both  the temperature and densities in the two cases differ greatly. Neither a temperature nor a density effect is expected theoretically in the for­mation o f  the pdp  molecule. In our most recent T R I­UM F measurement we observed the gamma-ray yield from  the p +  d fusion mediated by muons as a function o f density from  33 atm  to 100 atm  for a mixture o f 90% H2 +  10% D 2. In the same experimental system we measured the gamma-ray yield at 50 atm between 78 K and 373 K. A ll the new measurements were done on the M13 channel. Our earlier results were obtained on the old M20 channel. The switch to M13 from  M20 required a com plete redesign o f the data acquisition electronics and the data analysis package. In addition we made extensive changes to the high pressure gas target, including a new high pressure cell. The results from  M20 and M13 are thus from  nearly independent experiments. Our earlier M20 data showed a tem pera­ture dependence from  150 K to 500 K with the target at a room  temperature equivalent density o f 50 atm. Our newest results extend the temperature scan to lower values o f  temperature. We observed the temperature dependence again, as seen in Fig. 16. However, there does not seem to be a pressure dependence within a factor o f  two, as seen in Fig. 17. The 33 atm point seems to be off, but this is unresolved yet since we also see an anomaly in the muon decay electron counts at this pressure.l 4 . 03 .53 .0■ 2 .5 1—100 200 300 400 tem peraturcC °K )Fig. 16. Normalized gamma-ray yield vs. temperature. Den­sity equivalent to 50 atm at 300°K.600p re s s u r o C p s l)1000 1500Fig. 17. Normalized gamma-ray yield vs. gas density. The 33 atm point is suspect.During the run we also attem pted to determine the impurity concentrations in the gas. We did this by de­liberately contaminating the gas m ix with N2 to the level o f 100 ppm . By com paring the fusion gamma- ray yield from  the contaminated gas with the “pure” gas and using measured transfer rates for p ~ d  +  Z  —* d + Z p ~  we limited the nitrogen-equivalent contamina­tion in our sample to 22±32  ppm . We hope that further analysis can lower the error bounds on this number.We hope to continue our measurements up to about 1000 atm  using the L A M P F /IN E L  gas target. This target can also run from  10 K to 300 K. W e also will be com paring the anomalous behaviour o f HD at these extremes o f pressure and tem perature to what we first observed in our M20 data on HD.20E xperim ents 442, 556T h e  4H e,208P b (x + , x+ x _ ) reaction  atTn+ =  280 M eV(D. Vetterli, UBC; N. Grion, IN F N -T rieste)During a two-month period o f  high intensity-beam this fall we perform ed a (7r,27r) measurement on 4He and 208Pb at T^+ =  280 M eV using the T R IU M F M i l  channel. This experiment is a continuation o f  the A (tt, 2n)A ' research program  aimed at studying the pion-induced pion production over a wide range o f  nu­clei. As the 208Pb target was not fully examined dur­ing the run in summer 1988 we com pleted the data set by covering the second half o f  the allowed run in the reaction plane phase space. T he data obtained from this second independent run allow checking for sys­tem atic errors. The com plete set o f  data will test the A (tt, 2tF)Ai m odel o f  Oset and Vicente-Vacas [Nucl. Phys. A 4 5 4 , 637 (1986)] as well as the prediction o f an enhancement o f  the cross section due to pre-critical pion condensation in nuclei as suggested by Cohen and Eisenberg [Nucl. Phys. A 3 9 5 , 389 (1983)]. The m otivation for the measurements on 4 He was to fur­ther investigate the observed differences between the four-fold differential cross section on 160  [Grion, Nucl. Phys. A 4 9 2 , 509 (1989)] and on D 2. The low energy enhancement o f  the 7r+ spectrum  o f  160(7r,27r) shows a striking difference from  the results o f  the 2H (x, 2n)pp experiment. A  possible explanation could be the con­densation o f  two-pion pairs in the nuclear medium that is presently under investigation. Furthermore there is a significant difference in total cross section for 160  and 12C [Ravah, Ph.D . thesis, Tel-A viv University, O ctober 1989] o f  about a factor o f  three. Whereas in 160  the cross section is about six times bigger than the one o f D 2, meaning that in oxygen nearly every neutron repre­sents an “effective reaction centre” for the (x ,2x ) pro­cess, the ratio toward the free process is much smaller for 12C. W ith  4He we have chosen the simplest nucleus that already shows average nuclear density. It is hoped that more refined calculations and treatment o f  nuclei, where the attenuation and strucure effects may be eas­ier to handle, may provide more conclusive results.The experimental details are already described in the last Annual Report (1988). In order to guaran­tee a more reliable measurement o f  the incident beam flux, we added upstream o f  the target another ho- doscope consisting o f  four horizontal strips. Because o f  the lower beam  flux (~ 1 3  MHz) we were able to run also a single scintillator equipped with a fast base as a beam  counter. A ll beam counters were calibrated against each other as a function o f  flux and all o f  them showed linear behaviour up to the nominal flux. The Q Q D  spectrom eter was used to detect the outgoing x~in the energy range o f  20-100 M eV at lab angles 30°, 50° and 80°. T he C A R U Z, covering lab angles from 25°-125°, detected the x + in coincidence with QQD in the energy range 8 -75  M eV. The new data are now being analysed.E xperim ent 446 P ion -p ro ton  brem sstrah lung(P . Kiiching, TRIU M F/Alberta; A . Stetz,Oregon State)One o f  the goals o f  studying radiative x+-proton  scattering is that it may be possible to extract the magnetic m om ent o f  the Delta. The first experiment, which was perform ed by a group from  UCLA in the 1970s [Sober et a l,  Phys. Rev. D 11, 1017 (1975); Nefkens et al.., Phys. Rev. D 18, 3911 (1978); Leung et a l, Phys. Rev. D 14, 698 (1976); Smith et a l, Phys. Rev. D 21, 1715 (1980)], looked at several pion en­ergies and photon angles and found that the differen­tial cross section falls uniform ly with increasing pho­ton energy. This is contrary to what one expects from model calculations based on a straightforward appli­cation o f  the soft photon approxim ation (SPA) [Low, Phys. Rev. 110, 974 (1958)], where a visible bump is predicted at higher energies due to the delta resonance [Fischer and Minkowski, Nucl. Phys. B 36, 519 (1972); P icciotto, Nucl. Phys. B 89, 357 (1975); Haddock and Leung, Phys. Rev. D 9, 2151 (1974)].Over the years it has becom e clear that the amount o f  destructive interference between the contributing amplitudes, which has to take place in order to re­produce the data, is quite sensitive to how unitarity and gauge invariance is maintained in the model as one goes from  the elastic case to the radiative process. One approach has been to further develop the SPA [Nefkens and Sober, Phys. Rev. D 14, 2434 (1976); Landi and Matera, Nuovo C im ento 6 4 A , 332 (1981); Liou and Ding, Phys. Rev. C 35, 651 (1987)], whereas others have concentrated on m icroscopic isobar models [Beder, Nucl. Phys. B 84, 362 (1975); Pascual and Tar- rach, Nucl. Phys. B 134 , 133 (1978)]. The most recent calculations o f  the latter type are due to groups from M IT  [Heller et a l, Phys. Rev. C 35, 718 (1987)] and T R IU M F  [W ittm an, Phys. Rev. C 37, 2075 (1988)]. The M IT  group developed a consistent, nonrelativistic, fully dynam ic and gauge-invariant model with struc­ture functions suggested by a cloudy bag model cal­culation. The T R IU M F  calculation was based on a relativistic formalism, where the difficulty o f  struc­ture functions was avoided by using a R -m atrix  type approach. This method allows one to unambiguously maintain unitarity and gauge invariance for the inelas­tic process. Both models have done equally well at re-21HorizontalD riftChambersT rig g e r and TOF countersA lb e rtaHorizontalDriftChambersPacmanC-MagnetSpectrom eterProton Detector » Array o f  Plastic San tHla torsFig. 18. Experimental set-up for the bremsstrahlung experimentproducing the available cross-section data, whereas the two calculations can differ by as much as 30% in the predicted asymmetries. In both  models the asymmetry is quite sensitive to  the magnetic moment o f the delta.Our experiment was set up at T R IU M F  during the fall o f  1988 on the M i l  channel. We took our first data during the month o f  January and com pleted data- taking in early April. The experimental configuration (Fig. 18) was designed to be sensitive to the differences in the above-m entioned m odel calculations as well as to cover a large range o f angles in coplanar geometry complementary to a recent experiment at PSI [Meyer et al., Phys. Rev. D 38, 754 (1988)].The target was the T R IU M F  frozen spin polarized proton target (F S T ) [Delheij et a l, Nucl. Instrum. M ethods A 2 6 4 , 186 (1988)], which had been equipped with a pair o f  Helmholtz coils in place o f  the usual hold­ing field coils in order to increase the accessible range o f angles in the scattering plane. It was run at an average polarization o f  80% with an average lifetime o f 200 h. Photons were detected in one o f three large N al(T l) crystals. T IN A  and M INA were kept at 150° and 105°, respectively, whereas A LB E R TA  was moved between 65° and -1 4 0 °  with respect to the beam. The proton detector consisted o f  an array o f  11 plastic scintillatorblocks, each 5.5 in. long and 4° in width. The accep­tance was designed to com plem ent the acceptance o f the pion spectrom eter. A  0.5 cm  thick dE/dx counter in front served for particle identification (Fig. 19). The pion spectrom eter consisted o f  the PAC M AN  magnet with a pole gap o f  30 cm  and a set o f  four T R IU M F- built horizontal drift chambers. Due to the large gap relative to the pole width (68 cm ) the magnet had to be equipped with field clamps. The m agnet’s centrelineProton kinetic energy [MeV]Fig. 19. Proton detector: dE/dx versus T.221050Tor8506 5 0 -45025050T =20 MeVp' P.'s g5 MeV207r‘s60 100 140 180 220Pion kinetic energy [MeV]260Fig. 20. PACMAN spectrometer: Time of flight versus Tn.was placed parallel to the beam  line at a distance o f 130 cm , giving a solid angle o f  approxim ately 80 msr. The range o f  accessible pion angles for both data runs taken together was estimated by M onte Carlo methods to span from  70° to 110° (counted here as negative). Figure 20 shows a p lot o f  time o f  flight versus apparent pion kinetic energy, which serves to identify pions and protons in the spectrom eter.The January run was divided into a data-taking phase on the FST, a background target phase on the FST with carbon beads substituted for the bu­tanol beads, and a calibration phase on a LH2 target. The beam  flux o f  approxim ately 2 x  1077r+ / s was m on­itored indirectly by several complementary methods. Together with the April run, we expect to have accu­mulated about 200 h o f  data, or roughly l x l O 5 npy  events.Data analysis is in progress.E xperim ent 453M u on ic  h ydrogen  in vacuum(G .M . Marshall, TRIU M F)M uonic hydrogen isotopes (p~ p , p ~ d  and p ~ t)  are potentially very useful for the study o f  fundamental electroweak and strong interactions. The limitations normally im posed by the production medium (gaseous and liquid hydrogen targets) could be overcome by a production technique which allowed the atom s to exist essentially in vacuum. Experiment 453 was proposed in order to determine whether this might be made pos­sible by the ejection o f  muonic hydrogen from  a thin layer o f  solid hydrogen in vacuum. Initial estimates o f rates were based on cross sections for the interaction o f  muonic hydrogen with hydrogen molecules and on the initial kinetic energy distribution, neither o f  which had been measured unam biguously at the time. Theexpected signals were low, but it was hoped that back­grounds could be reduced to a level which might allow the observation o f  em itted m uonic atoms.The detection system was based on determining the position and time o f  muon decay via the decay elec­tron, using delay line wire chambers and scintillators and M IN A to discriminate against low-energy electrons to reduce background and im prove position resolution. A  cryostat was constructed to freeze a hydrogen layer and hold it at 2.5 K. The initial beam  period in January provided startling results, namely that negative muons in the form  o f  neutral m uonic atom s were emitted from a natural hydrogen layer (about 100 ppm  deuteron con­centration) with a yield many times that expected. In addition, the yield was observed to increase as the layer was made thicker (F ig. 21) until saturation was reached at a thickness corresponding to a mean attenuation length o f  2.5 m g -cm "2. The speed o f  the emitted sys­tem corresponded to energies o f  a few eV  for muonic hydrogen.The correct interpretation o f  this result was reached after a second beam  period in June, which confirmed the emission into vacuum. T he muon is emitted from the layer in the form  o f  m uonic deuterium (p ~ d ), fol­lowing initial form ation o f  p ~ p  and subsequent transfer o f  the muon to a deuteron. The transfer process results in a kinetic energy for p~  d o f  about 45 eV. It also hap­pens that there is a very pronounced minimum in the cross section for interaction o f  p ~ d  with H2 (a man­ifestation o f  the Ramsauer-Townsend effect in quan­tum scattering processes) at an energy o f  a few eV, so that the hydrogen film becom es almost transparent to passage o f  p~ d . The m ost recent beam  period for the experiment was in Decem ber, when it was confirmed that emission did indeed depend on the concentration o f  deuterons in the layer, and was below the limit o f sensitivity when protium  (less than 1 ppm  deuteron0  1 2 3 4 5 6 7 8T h i c k n e s s  ( m g  c m  2)Fig. 2 1 . Dependence of the emission signal on hydrogen layer thickness.23Pion c .m . angleFig. 22. Analysing powers at Tp =  400 MeV for the reac­tion D(p, r~pp)p  from the first run of this experiment. The horizontal error bars represent the width of distributions within bins of pion c.m. angle, the vertical error bars are statistical uncertainties. The solid and dashed lines are pre­dictions of the 2 partial wave solutions from Piatsetsky et al.Fig. 23. Preliminary analysing power results from cur­rent work at 353 MeV (squares), 403 MeV (triangles) and 440 MeV (circles). These are preliminary results calculated on line during the experiment. 9 is the equivalent centre- of-mass angle for the pion spectrometer setting. Further analysis will divide each angle into three sub-ranges. The solid curve is the same as that in Fig. 2 2 .concentration) was used as a target. Results were also obtained on the attenuation o f  p~ d  in a layer o f  pure D 2 frozen to the surface o f  natural hydrogen; these are being analysed to extract the cross section.The emission can be used to measure parameters (such as the cross sections) o f  some interest to the un­derstanding o f  m uon-catalyzed fusion. Other experi­ments in pC F  are also feasible, some o f which demand the preparation o f  com posite targets in special geome­tries. Together with the liberation o f a free negative muon following a fusion interaction, this experiment may also lead to a source o f slow p.~ suitable for reac­celeration in a beam  o f very low m om entum  spread. These possibilities will be pursued in the com ing year.E xperim ent 460pn <-♦ x_ pp(15o)(P . Walden, TR IU M F)Experiment 460 ran on beam line IB  for 45 sched­uled 12 h polarized beam  shifts from  August 11 to September 25. Not all shifts were useful for the ex­periment as there was an unusual number o f  shifts lost due to cyclotron downtime.This was the second run for the Expt. 460 collabo­ration which had a first run during September 1987. The experiment looks at the D (p ,n ~ p p )p  reaction (quasifree pn  —*• n~ p p (x So)) using a liquid deuterium target, the Q Q D  spectrom eter to detect the n ~ , and a large scintillator hodoscope to detect the two pro­tons. The Tel-A viv bars, used in many other TR IU M Fexperiments, served as the proton detector for the sec­ond run. T he first run in 1987, as it turned out, was basically a feasibility study at 400 M eV. The second run used beam  energies o f  353, 403 and 440 M eV and collected much more data.The ob ject o f  the first run was primarily to deter­mine which o f  the two PW A  solutions [Piasetsky et al., Phys. Rev. Lett. 57 , 2135 (1986)], determined from 3H e(7r- ,p n )n  (quasifree 7r_ p p (15o) —* pn) absorption cross sections, appeared to be the m ost probable. The PW A  predicted dramatically different pion analysing powers, A no , for the pn  —*• n ~ p p ( 1 So) reaction. The results o f  the first run are shown in Fig. 22. T he mea­sured A no clearly favours the solution with a sizeable 3 Si —i-1 Pi ampliltude (the “ S”  solution, solid line). This result has now been published [Ponting et al., Phys. Rev. Lett. 63 , 1792 (1989)].The primary ob ject o f the second run was to collect com plete angular distributions o f  cross sections da/dFl and A n 0  data for a com plete PW A. In Fig. 23 there is a com pilation o f the preliminary A „ 0 data for the pn —* n ~ p p (xSo) reaction that was measured on line. The improved statistics, except for one point, should be evident on a com parison with Fig. 22. That one poor statistics point, however, represents only a par­tial analysis o f  the com plete data set. The importance o f  a com plete angular distribution can be seen in the 440 M eV data where the crossover o f  the A no to neg­ative values above the c.m . angle o f  120° can only be due to partial waves involving D -wave pions (i.e., am­plitudes not considered in Piatsetzky et al.).24E xperim ent 470S tretch ed  states excited  in (n ,p) reactions on14C , 26M g  and 30Si(J .W . Watson, K ent State)In November we measured spectra for the 1 4 C (n ,p )  and 26M g(n , p ) reactions at 280 M eV beam  energy, with the C H A R G E X  facility in the proton hall. The 14C target contained 3.5 g (17 C i) o f  14C powder plus small amounts o f  12C, 160  and other light elements; this target was on loan from  Los Alam os National Lab­oratory. The 26M g target was a 19 g sample (enriched to 99.46% ) o f  26M g on loan from  the Research Materi­als Collection at Oak Ridge National Laboratory.T he focus o f  this experiment is the study o f T =  2 “stretched” particle-hole states, specifically the ( ^ 5/ 2) 7rP3/ 2) 4 -  state excited in 14B and the ( ^ /7/ 2, ‘lrd5 / 2 ) ~ 1 6“  state excited in 26Na. To excite these high-spin states data were taken in the mom en­tum  transfer range from  1.5 to 2.5 fm _1 ( 6  =  19°-35°). Analysis is under way at Kent; this project is part o f the doctoral dissertation research o f  X iao-dong Hu, a graduate student at Kent State University.E xperim ent 482M easurem ents o f  spin  transfer coefficients in pd e lastic sca tterin g(R . Abegg, TR IU M F)This experiment received 11 shifts o f  normal, side­ways, and longitudinally polarized beam time to mea­sure angular distributions o f  spin transfer coefficients in pd elastic scattering at 200, 300 and 400 M eV. T w o shifts were lost due to outside interference in the form  o f  the introduction o f  a malfunctioning branch coupler for another experiment. For financial reasons, it was also decided to fill the vault solenoids locally which, with retuning and m andatory checks for unwanted com ponents, amounted to an additional lost shift. It also turned out that the carbon background from  the C D 2 target was more severe than originally estimated. Therefore, in the remaining 8 shifts pd elastic scatter­ing data as well as carbon background runs were taken at 200 M eV for M RS laboratory angles o f  20°, 30°, 40°, 50° and 60° for incident normal, sideways, and longitudinally polarized protons. In the off-line anal­ysis great care was taken in the subtraction o f  the carbon background. The asymmetries corresponding to the parity-forbidden normal-to-sideways spin trans­fer (proportional to D ns) were extracted and shown to be consistent with zero. The analysis o f  the data to extract the spin transfer coefficient D nn is almost com plete and indicates that at large proton laboratory angles D nn is flat and about one, but at forward anglessignificant deviations from  one seem to be occurring. Data at 800 M eV published by Igo et al. show the same trend although no deviation from  one is reported. At 500 M eV data from  the same group show the angular distribution o f  D nn to  be again flat but with values consistently below one (~ 0 .8 ). Due to this variation as a function o f  energy in the data sets from  UCLA and T R IU M F , and the small-angle behaviour o f  the angu­lar distribution o f  the T R IU M F  set, theorists became interested in calculating spin-transfer parameters for pd elastic scattering.We have com pleted one-third o f  the experimental data-taking in slightly over one-half o f  the beam time originally requested. W e have requested 14 additional shifts o f  normal, sideways, and longitudinally polarized beam at 400 M eV (8 angles) and at 300 M eV (7 angles) to com plete the experim ent, and we expect this to oc­cur in the fall o f  1990. To drastically suppress the car­bon background, we intend to use a plastic scintillator inside the scattering chamber to detect the associated deuterons in coincidence with protons selected by the M RS. Even though the data acquisition system is still limited by the m icroprocessor (the J l l ) ,  we expect an enriched data sample.E xperim ent 49145S c(n ,p )45C a and 45S c(n ,p )45T i: A  significant test o f  m odel ca lcu lations in the (fp ) shell(W .P . Alford, W estern Ontario)In the (sd ) shell it is feasible to carry out model calculations using an unrestricted (sd) model space. As a result, the effective tw o-body interaction used in shell model calculations is well determined and calculations o f  a wide range o f  observables show good agreement with experiment.In contrast to this situation, in the ( f p )  shell calcu­lations in the full m odel space have not been feasible, and various truncation procedures have been used in order to proceed with calculations. T he effective two- body interaction is not well determined, and compar­isons between calculations and experimental results of­ten show large disagreement.A  measurement o f  G T +  strength in the 45S c (n ,p )45Ca reaction should permit a critical com ­parison with m odel calculations. The nuclei involved have five particles in the ( f p )  shell, but the relatively large isospin o f  both nuclei reduces the dimensionality o f  the model calculations so that they can be carried out in an unrestricted ( f p )  space. This possibility then permits a search for a suitable effective interaction for the full m odel space, and will allow a study o f  the m od­ifications needed as the space is truncated.Measurements o f  the 45S c(n ,p ) reaction have been25carried out at 20 M eV at angles o f  0°, 3°, 6°, 9°, 12°, 15° and 18° with an overall energy resolution o f  1 M eV. T he spectrum  at forward angles shows peaks near the ground state and at about 5 M eV excitation, which appear to  arise from  G T +  transitions. The transition at 5 M eV is predicted by available calculations but the “ground state” transition is not. Since the Q  value o f the ground state transition is 0.535 M eV, background from  the H (n ,p ) reaction is a serious problem  at for­ward angles, and careful analysis is required to extract the strength o f  the transition o f  interest. This is now in progress.Measurements o f  the 45Sc(p, n )45T i reaction have re­cently been carried out at IU CF, so that we do not plan to repeat this measurement at T R IU M F .E xperim en t 502M easurem ents o f  analysing pow ers in low -en ergy  xd elastic sca tterin g(N .R . Stevenson, Saskatchewan)The irN N  system has been the subject o f  a great deal o f  theoretical and experimental effort in recent years. Access to understanding this system is afforded through several scattering processes, xd scattering has been shown to be one o f  the m ost sensitive reactions to many o f  the remaining outstanding problem s such as the effect o f  the ttN P n  potential [Morioka and Afnan, Phys. Rev. C  26, 1148 (1982)], the degree o f Pauli blocking in the N N * intermediate state [Afnan and M cLeod, Phys. Rev. C 31, 1821 (1985)], and the possibility o f  exotic structures such as dibaryon reso­nances [Grein and Locher, J. Phys. G 7 , 1355 (1981); Locher and Sainio, Phys. Lett. 121B , 227 (1983)].Over the energy range 100-300 M eV the xd elas­tic process is dominated by the ttN P 3 3  intermediate- state potential. For this reason a concentrated effort has been made to accumulate elastic scattering data (cross sections, vector and tensor analysing powers and polarizations, and spin-transfers) over this energy re­gion. By subsequent phase-shift or amplitude analyses the underlying fundamental mechanisms o f  this and its related n N N  system will becom e better understood.Probably the least well understood mechanism in xd elastic scattering is the contribution o f  the inter­mediate n N  P n  term. After factorization into pole and non-pole terms, to  account for real pion absorption and rescattering, respectively, the dependency o f  many (particularly tensor) observables are found to critically depend on exactly how this factorization is done and the extent o f  Pauli blocking in the N N *  system. Since the P n  contribution is small (in magnitude) compared to the P3 3  at higher energies, its effect is somewhat difficult to extract with certainty from  experimentalmeasurements. For this reason a program  o f  measure­ments o f  analysing powers at 50 M eV was undertaken.Experim ent 502 involves scattering pions produced in the M13 channel o ff o f  a polarized deuterated bu­tanol target. The scattered pions are detected in the Q Q D  spectrom eter. T he first running period o f this experiment (summer 1988) was ham pered by target problem s but eventually saw the measurement o f three angles (d'Tab =  70°, 90°, 130°) with a vertically polar­ized target. The results for the vector analysing power iT n  were presented in last year’s report.During this year the polarized target was modified to increase the “signal-to-noise” o f  the xd  elastic reac­tion. Previously, the deuterated butanol was contained in a mylar basket as beads immersed in the refrigera­tion liquid (3H e /4He). The volume o f  coolant was 3 -4  times that o f  the target as viewed by the beam. As helium is the worst contaminant in detecting xd  elas­tic events (closest in the m om entum  analysed by the Q Q D ), we were restricted to  larger angles (0]rab > 7 0 °) in our measurements. By constructing a solid slab tar­get (6 m m  thick) and by constraining the coolant to 2 m m  on either side o f  the target, a vast improvement in the quality o f  the observed spectra was obtained. W ith  this design we were able to measure the com ­plete range o f  angles that was originally proposed. In December we collected data on four further x + d angles: 0*xab =  50°, 60°, 80°, 100°. Analysis is in progress.Charge sym m etry breaking in the xd  elastic system has been the subject o f  considerable effort in recent years [Smith et al. Phys. Rev. C 38, 240 (1988)]. A t T R IU M F  there is an ongoing experim ent (399) that is determining the ratios o f  cross sections for x + d and x _ d elastic scattering at low (M 13) energies. Extrac­tion o f  parameters describing the width and masses o f  the delta isobars are objectives o f  this experiment. However, several corrections and assumptions have to be made in order to evaluate these parameters. Some, such as the effect o f  the Coulom b potential, are non­trivial. In order to supplement and enhance our abil­ity to more accurately extract these fundamental pa­rameters Expt. 502 will also measure iT n  for x _ d in the spring o f  1990. Theoretical analysis [Frolich et al., Nucl. Phys. A 4 3 5 , 738 (1985) and private communi­cation] has shown that iT n  is the m ost sensitive ob ­servable to the (external) C oulom b interactions, and its measurement in both x + d and x - d would provide the most useful contribution for the ongoing theoret­ical interpretation o f  the effects o f  charge symmetry breaking in this system.26E xperim ent 535A  search for deep ly  b ou n d  p ion ic  states in 208P b  using the (n ,p x~ )  reaction  at T„ =  418 M eV(T . Yamazaki, Tokyo)A  recent paper by Toki and Yamazaki [Phys. Lett. B 213, 129 (1988)] suggested that a charge exchange reaction such as (n ,p )  might be used to populate the deeply bound states in heavy pionic atom s. Their cal­culations, essentially consistent with earlier ones by Friedman and Soff [J. Phys. G : Nucl. Phys. 1 1 , 37 (1985)], predict that in pionic 208Pb the Is  state should be bound by 7.0 M eV and exhibit a width o f  0.7 MeV. M oreover, Toki and collaborators predicted, using the plane wave impulse approxim ation, that the deeply bound states in 208P b-7r~ could be populated in the 208P b (n ,p ) reaction with a cross section on the order o f  1 m b/sr.A  measurement o f  the 208P b (n ,p )  cross section was undertaken at T R IU M F  using the C H A R G E X  facility to look for the lowest bound states o f  the lead pionic atom . These states are expected to appear as narrow structures in the (n ,p )  spectrum  at excitation energies in the region o f  135 M eV, just below the threshold for the production o f  free pions. Because o f  the large ex­citation energy for these states the measurement was done in several stages. The 208P b (n ,p ) and H(n ,p )  re­actions from  0-180 M eV excitation were measured us­ing the full 420 M eV achromatic primary beam  with an overall resolution o f  « 2  M eV. Three M RS dipole field values were required to span the full excitation energy range. The yield from  the H (n ,p ) ground state peak together with the known value o f  (53.7 m b /sr) for this cross section were used for an absolute cross section normalization for the 208P b (n ,p ) measurement. The full H (n ,p ) response provided a measure o f  the neu­tron lineshape for the 7Li(p, n ) reaction which, when deconvoluted from  the measured spectrum, yielded the 208P b(n , p) response for m onoenergetic 418 M eV neu­trons.A measurement o f  the 208P b (n ,p ) cross section in the region o f  the 208P b-7r~ bound states with good resolution was necessary in order to resolve the dif­ferent pionic atom  states from  each other and from  the background continuum. This high-resolution measure­ment o f  208P b(n , p) was obtained with a momentum- dispersed ( 6 x / (6 p/p) =  - 6  c m /% ) proton beam  on a 7 m m  strip 7Li target. The resolution, measured at the same m om entum  as the outgoing protons from  the Pb ■ 7t”  system  using the H (n ,p ) reaction at 280 MeV, was 1.15 M eV FW H M . The neutron tail deconvolu­tion and the absolute cross-section normalization for the high-resolution data were obtained by comparison with the same excitation energy region o f  the achro­m atic 208P b (n ,p ) response. Such a deconvoluted andFig. 24. A spectrum of the 208Pb(n ,p) response in the re­gion of the expected pionic atom bound states. The res­olution was 1.15 MeV FWHM. The abscissa corresponds to the excitation energy in the 208 Pb ir~ system less the pion mass. Shown inset are the calculations of Toki et al. convoluted with a 1 MeV lineshape width.normalized 208P b (n ,p ) spectrum  is shown in Fig. 24.A  x 2  search was carried out to establish an up­per limit for the pionic atom  bound-state cross sec­tion. A  third-order polynom ial was fit through the spectrum  excluding the data in the region between 125 «  140 M eV where the states o f  interest are ex­pected to lie. W ith  the background fixed a peak search was done using a 1.15 M eV FW H M  Gaussian, allowing the position and height to vary. W ith this procedure an upper limit o f  0.3 m b/sr, with a 90% confidence level, was obtained for the production o f  bound pionic states in the 208P b (n ,p ) reaction.The original m otivation for this measurement stemmed from  a plane wave calculation for the 208P b(n , p )208Pb -n~ reaction by Toki et al. shown in­set in Fig. 24. Their cross section is an order o f  magni­tude larger than the upper limit obtained in this mea­surement. Subsequent to this result, a more complete calculation including effects o f  distortions in a rela- tivistic framework [Cooper et al., Nucl. Phys. A 4 7 0 , 523 (1987)]. This distorted wave calculation, shown in Fig. 24, is consistent with the measured upper limit o f  0.3 m b /sr for the cross section o f  the lower bound states o f  the 208Pb pionic atom .E xperim ent 536T h e  6Li(/i~ , 2<)i/m reaction(Y .M . Shin and N.R. Stevenson, Saskatchewan)Muon capture on a 6Li nucleus has been highlighted as a possible reaction to determine the muon neutrino27mass [Mintz et a l,  Phys. Rev. C 20, 286 (1979)]. The reaction cross sections near the endpoint (where tri­tons are “back to back” ) is unknown but is expected to be small [Junker, Nucl Phys. A 4 0 7 , 460 (1983)]. In order to estimate this and also to extract information on the internal nature o f  the 6Li nucleus, such as the spectroscopic factor for the (t +  3He) cluster configu­ration, Expt. 536 will determine the cross section for this reaction over a large angular range.This experiment proposes to study this reaction with a series o f  plastic A E -E  counters an d /or with solid- state counters. In order to determine the required and optim um  inform ation to be obtained in this experi­ment, a test run was undertaken in the summer in the M13 channel using a plastic A  E -E  arm in coin­cidence with a solid-state arm consisting o f  a thin SiLi (0.5 m m ) counter and a thick Ge stack o f  counters. T w o pairs o f  wire chambers were also employed to de­termine the effect o f  angular resolution in the actual measurement. On-line analysis showed a clear signal for the ditriton reaction. The analysis o f  this data is under way.E xperim en t 538 M easurem ent o f  u / B g t  fo r  13C (J. Mildenberger, SFU)The relation o f  the transition m atrix elements in­volving the isovector com ponents o f  the nucleon- nucleus interaction to weak-decay m atrix elements has received much attention, both theoretically and exper­imentally. Such a relationship, if  it could be reliably demonstrated, would enable the investigation o f weak- decay processes into energetically forbidden regions, as well as leading to a greater understanding o f  nuclear re­action mechanisms themselves [Taddeucci et al., Nucl. Phys. A 4 6 9 , 125 (1987)]. O f particular im portance is the hypothesis that a / B q t  is the same for all tran­sitions from  a given target for (p ,n ) , (n ,p )  and (p ,p ') reactions, when isospin and kinematic factors are taken into account.A  recent in-depth study o f  the relationship o f  (p, n) cross sections at small angles to the corresponding /?- decay transition states [Taddeucci, op. cit.] found that for L = 0 spin-flip transitions in the D W IA  model, the cross section could be expressed as<Tpn(<?)w =  &g t ( A ) F ( q , u > ) B Gr £ ( A , a )  ,where q is the m om entum  transfer, u  is the energy loss and a  specifies the final state o f  the recoil nucleus. F(q,u>) is a form  factor, calculable in the D W IA  model, which approaches unity as q and u  approach 0. Since <j~T (referred to as the “unit cross section” ) can also be calculated in the D W IA  model, direct comparisons canbe made between experimental measurements and the­oretical predictions. It is widely acknowledged that the observed relationship between nuclear iso vector tran­sitions and /?-decay processes is a very useful tool and warrants further investigation; its full potential has not yet been realised.Perhaps the most crucial element o f  the theory is that ( t / S q t  is independent o f  the particular transition for a given target nucleus, as many inferences may be made based on the value found for cr/B qt f ° r a single transition; certainly transitions to states in the same isospin multiplet should have the same ct/ B gt ratio, independent o f  the details o f  the particular model. It is thus o f  great im portance that a value determined for a given target be reliable. Recent (p, n) results from  IUCF for 13C ( < t ( p , u ) / B q T  =  14.7 ±  1.1 for the tran­sition to the 15.1 M eV 13N state) [Taddeucci, op. c it ]  are in disagreement with the (n ,p )  results from  T R I­UM F (a (n ,p )/ B ^ r  =  10.97 ±  0.56 for the transition to the 13B ground state) [Jackson et al., Phys. Lett. B 201, 25 (1988)]. The main aim o f  Expt. 538 was to mea­sure the ratio a (p ,n )/ B q T at 0° for the 13C(p, n )13N charge exchange reaction at 200 M eV for transitions to the 15.1 M eV and ground states o f  13N, and thus attempt to resolve this discrepancy.It should be noted that while the T R IU M F  result uses the experimentally measured f t  value for the 13B to 13C ft decay, there is no analogous /? decay from  13N to 13C. Further, there is a large ( « 2 3 % ) asym­metry in the f t  values for the mirror decays in the A = 13  system: lo g /<  =  4.10 for the 130 ( /9 + )13N (g.s.) transition, and 4.01 for the 13B(/? ) 13C (g .s.) transi­tion. The value o f  f t  used by the IU CF group in their calculation o f  a (p ,n )/ B ^ T is thus necessarily subject to a considerable uncertainty. They chose to use the 13B (/?“ ) value, modified by the measured rate asym­metry for the A = 12  system. Taddeucci et al. argue that this should be a reasonable estimate, based on the similarities in the structure amplitudes and energy systematics o f  the 12C -  12N (g.s.) and 13C -  *3N(15.1 M eV ) transitions. After including the appropriate spin and isospin factors, they get B q T =  0.23 ±  0.01, the uncertainty being sim ply the difference in the asym­metry parameters for the A —12 and A=C3 systems. But with such large asymmetry, it would be reason­able to assume an uncertainty larger than that quoted. But regardless o f this, the discrepancy between the two tt/Bg t  values is still significantly larger than can rea- sonbly be accounted for by the f t  asymmetry.As well as the (p, n ) measurements, we will ob­tain the < t (p ,p ') /R g t  ratio ( the (P ’ P') anal°g  to <r{n,p)/B%T and a (p ,n )/ B s T ) for (p ,p ')  inelastic scattering to the 15.1 M eV state o f  13C. These ratios should be the same as <r(p, n)/B<7T and a (n ,p )/ B q T28when kinematics and the isospin Clebsch-Gordan coef­ficients are taken into account, and thus provide addi­tional inform ation on the breaking o f  mirror symmetry in the A = 13  system.The (p, p ') measurements were performed to also de­termine the amount o f  12C contam ination in the tar­get: it is very im portant to measure any possible con­tamination o f  the 13C target by 12C, as the reaction Q -value for the 12C (p, n )12N ground-state transition is almost exactly the same as for the 13C(p, n )13N 15.1 M eV transition.The data for Expt. 538 were taken in mid-January. The replaying o f  the (p ,n ) data using the LISA data analysis program  has been com pleted, and the (p, p ') analysis is currently under way.Experiment 540Spin excitations in the deformed nuclei 154Sm,158 Gd and 168 Er(D. Frekers, TRIU M F; H.J. W ortche, TH Darmstadt)Below excitation energies o f  about 4 M eV strong low-lying M l  transitions in heavy deformed nuclei have been well established through numerous electron scat­tering and nuclear resonance experiments. These tran­sitions are excited by the orbital part o f  the magnetic dipole operator and are dom inated by convection cur­rents. This has recently been demonstrated by com ­paring with intermediate-energy proton scattering at low-m om entum  transfers [Frekers et al., Phys. Lett. B 218, 439 (1989)].Experimental data for M l transitions above 4 M eV are scarce. Though in the A = 100  and A = 200  region the existence o f  the A Tz — 0 com ponent o f  the Gam ow- Teller strength has been shown to be at about 8 M eV excitation energy in numerous nuclei ( 120,124Sn, 140Ce, 208P b) [Djalali et a l, Nucl. Phys. A 3 8 8 , 1 (1982); Laszewski et al., Phys. Rev. C 34, 2013 (1986), Phys. Rev. Lett. 61 , 1710 (1988)], the experimental data and the well deformed systems are limited to some electron scattering data on 158Gd and 168Er only [Dietrich et al., Phys. Lett. B 220 , 351 (1989)]. In case o f  the (e, e ') scattering no appreciable concentration o f  M l  strength above S ( M 1 ) / A £ I~  7.5 p ^ /M e V  at energies around7.5 M eV was found.The m otivation for Expt. 540 was twofold:( 1) probing the existence o f  noticeable spin strength below 4 M eV