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

Annual report scientific activities,1987 TRIUMF Jun 30, 1988

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TRIUMFANNUAL REPORT SCIENTIFIC ACTIVITIES 1987CANADA’S NATIONAL MESON FACILITY O PER ATED  AS A JO IN T  V ENTU RE BY:UNIV ERSITY OF ALBERTA SIMON FRA SER U NIVERSITY U NIVERSITY OF V ICTORIA  U NIVERSITY OF BRITISH COLUMBIAUNDER A CONTRIBUTION FROM  TH E NATIONAL RESEARCH COUNCIL OF CANADA J U N E  1988, ■ 'MTRIUMFANNUAL REPORT SCIENTIFIC ACTIVITIES 1987TRIUMF4004 WESBROOK MALL VANCOUVER, B.C. CANADA V6T 2A3OURCEIZEDOURCEBAT HOBIOMEDICALLABORATORY42 MeV ISOTOPE PRODUCTION CYCLOTRONMESON HALLM 9 ( T T / j j )2 0  U i )MESON HALL EXTENSIONINTERIM RADIOISOTOPE LABORATORYNEUTRONACTIVATIONANALYSISTHERMAL M ESON HALLNEUTRON SERVICEFACILITY ANNEXF O R E W O R DIn my second and final year as chairm an of the TR IU M F Board of M anagem ent I have been able to  appreciate m any of the qualities which drive this rem arkable project forward. These are excellent friends in O ttaw a and V ictoria, fine leadership, much hope and energy, and, above all, excellent science.The science is described in th is annual report. I t covers a wide range of im portan t research fields and continues to  accum ulate its share of kudos. For exam ple, we were very pleased to  note th a t in mid-1987 Professor Yam azaki received the Im perial Medal from  the E m peror of Japan . He is apparen tly  only the fourth  Japanese physicist so honoured, and a m ajor portion  of his citation  perta ins to  his m uon work a t TR IU M F.The vigorous steps forward of the cam paign for a KAON factory do count on friends in O ttaw a and V ictoria, and on their appreciation of the opportun ity  which th is project provides for C anada. T he strong support of the B.C. governm ent emerged during the year. Jo intly  O ttaw a and V ictoria explored foreign partic ipa tion  w ith positive results. T he KAON project is now ready for construction approval by O ttaw a. We should also record here the action by our federal m inister, the  Honourable Frank Oberle, in adding to  T R IU M F ’s base two million dollars during the course of 1987.TR IU M F continues to  abound in scientific leaders as is evident to  anyone who reads th is report or visits the project. T he leadership is m anifested not only among the experim ental spokesmen from  m any universities who have active program s at T R IU M F bu t also am ong those who use TR IU M F as a base for big experim ents abroad. It is these physicists who carry the m om entum  of T R IU M F and will lead it on to  the KAON project.P.A. LarkinC hairm an, Board of M anagem entT R IU M F was established in 1968 as a laboratory  operated  and to  be used jo in tly  by the University of A lberta , Simon Fraser University, the U niversity of V ictoria and the U niversity of B ritish Columbia. The facility is also open to  o ther C anadian  as well as foreign users.T he experim ental program m e is based on a cyclotron capable of producing three sim ultaneous beam s of protons, two of which are individually variable in energy, from 180-520 MeV, and  the th ird  fixed a t 70 MeV. The poten tia l for high beam  curren ts -  100 fiA a t 500 MeV to 300 /j,A a t 400 MeV -  qualified th is m achine as a ‘meson fac to ry ’.Fields of research include basic science, such as m edium -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 trea tm en t.T he ground for the m ain facility, located on the UBC cam pus, was broken in 1970. Assembly of the  cyclotron sta rted  in 1971. The m achine produced its first full-energy beam  in 1974 and its full current in 1977.T he laboratory  employs approxim ately 363 staff at the m ain site in Vancouver and 18 based a t the four universities. The num ber of university scientists, g raduate  s tuden ts and support staff associated w ith the present scientific program m e is about 530.V ICONTENTSIN TR O D U C TIO N  ..............................................................................................................................................................  1SCIEN CE DIVISION ........................................................................................................................................................  3In troduction  ..........................................................................................................................................................................  3Partic le  Physics ..................................................................................................................................................................  5Spin correlation param eter A yy in n-p  elastic scattering  .................................................................................  5A study  of the decay x  —► ev  ....................................................................................................................................  5R adiative m uon capture w ith the T P C  ...............................................................................................................  6M easurem ent of parity  violation in p-p scattering  ...........................................................................................  6M uonium -antim uonium  conversion ....................................................................................................................... 8R atio  of spin transfer param eters D t / R t in d(p ,n)pp  quasielastic scattering  ..........................................10Test of charge sym m etry in n-p  elastic scattering  a t 350 MeV .....................................................................11M easurem ent of K + —* x +v V ....................................................................................................................................12M easurem ent of K ~  —*Yy  ..........................................................................................................................................15T he SLD experim ent ....................................................................................................................................................15Nuclear Physics and C hem istry ...................................................................................................................................... 17In itia l studies of the (n , p ) reaction on light nuclei ........................................................................................... 17Isovector giant resonances in 208P b (n ,p )  and 120S n (n ,p ) ............................................................................... 17Polarization transfer in the  pp —* dir reaction .....................................................................................................18R elativ istic m edium  effects a t in term ediate energies ........................................................................................ 18S tudy of the ( x + , x +x ~ )  reaction on 160  , 28Si and 40C a a t T n = 240 and 280 MeV ........................... 19T he EELL effect in 4He .............................................................................................................................................. 20Spin transfer m easurem ents in x  + d —+j> + p  .................................................................................................... 20Energy dependence of T20 and r 21 in x d  elastic scattering  ............................................................................ 22E xcita tion  of “stre tched” particle-hole sta tes in charge exchange reactions.... ...........................................23Zero degree radiative capture of neutrons ............................................................................................................ 24Exchange effects in 0+ —» 0-  inelastic scattering  ...............................................................................................25A search for the  te tran eu tro n  ................................................................................................................................... 25Few-body physics via the x d  break-up reaction .................................................................................................27Gamow-Teller streng th  and giant resonances in 90Z r(n ,p ) a t 198 MeV .....................................................28Energy dependence of the  charge asym m etry param eter A(T,r,6) in x d  elastic s c a t te r in g .................. 28Study of 48T i(n ,p )  as a test of lifetime calculations for the double b e ta  decay of 48C a .....................31Energy dependence of the (p ,n )  cross section for 13C and 15N .................................................................... 31M easurem ents of spin observables using the (p ,p '7 ) reaction ....................................................................... 33M easurem ents of the spin ro ta tion  param eter Q as a test of Pauli blocking in proton-nucleusscattering  ..........................................................................................................................................................................35Gamow-Teller s trength  deduced from  (n ,p ) and (p, n) reactions on 54Fe a t 300 MeV .......................... 37T he (n ,p ) reaction on 56Fe and 58Ni ......................................................................................................................39Elastic x ± p  differential cross sections a t T n =  30 to  67 MeV ....................................................................... 39Q uasielastic scattering  from  12C and 160  ............................................................................................................ 41M easurem ent of x ± d  elastic scattering  differential cross sections a t Tx =  30, 50 and 65 MeV .........41Nuclear wobble in the rare earth  nuclei ................................................................................................................ 42Q uasielastic scattering  of I s  s ta te  nucleons in light nuclei .............................................................................42T he spin-isospin response of 48C a and 9Be from  the (n ,p )  reaction a t 200 MeV .................................. 43Research and developm ent studies w ith TISO L ................................................................................................ 44Com plete spin observables for quasielastic p roton scattering  from 54Fe a t 290 MeV ...........................45N eutron-proton charge exchange am plitudes ...................................................................................................... 48A study  of the Pauli blocking of Gamow-Teller transitions using the 70|72,74G e(n, p )70’72’74Ge reactions ........................................................................................................................................................................... 48T he np —> xd  cross section very near threshold ..................................................................................................48Isovector 1+ —► 0+ transitions in the A  =  6 system  .......................................................................................... 50Strangeness in nuclei v ia  the  ( x + , K +) reaction ................................................................................................ 51Research in C hem istry and Solid-State Physics ........................................................................................................ 53Pionic chem istry ............................................................................................................................................................53M uon m olecular ions and ion-molecule reactions ...............................................................................................53High pressure m uon spin resonance in liquids .................................................................................................... 55Resolved nuclear hyperfine s truc tu re  of anom alous m uonium  in sem iconductors ...................................56M uonium  in micelles .................................................................................................................................................... 58/xLCR spectroscopy of free radicals ........................................................................................................................ 59Reactions of m uonium  w ith halogen ...................................................................................................................... 60M uon catalyzed fusion in HD and H 2+ D 2 gaseous m ixtures .........................................................................61Level crossing resonance of m uonium  radicals in micelles ..............................................................................61M uonium  and m uon sta tes via rf  resonance ........................................................................................................ 62/xSR studies of sub- and supercritical fluids .........................................................................................................65M uon spin ro ta tio n  studies of dioxygen and ethylene on silica powder ..................................................... 66p S R  study  of antiferrom agnetism  and high-tem perature  superconductivity  ........................................... 67T heoretical program  .......................................................................................................................................................... ..In troduction  ....................................................................................................................................................................70Nuclear struc tu re  .......................................................................................................................................................... 70Proton-induced reactions and scattering  .............................................................................................................. 71Few-nucleon processes ..................................................................................................................................................72Pion physics ....................................................................................................................................................................73Kaon p h y s ic s ................................................................................................................................................................... 74Electron scattering  ........................................................................................................................................................75Sym m etry breaking ...................................................................................................................................................... 76QCD and quark models ..............................................................................................................................................77Lattice gauge calculations ..........................................................................................................................................78Electroweak in teractions ............................................................................................................................................ 79M uon spin ro ta tion  ...................................................................................................................................................... 80A PPL IE D  PRO G RA M S DIVISION .............................................................................................................................81In troduction  .................................................................................................................................................................... 81Biom edical program  ......................................................................................................................................................8142 MeV cyclotron fa c i l i ty ............................................................................................................................................85R adioisotope processing (AECL) .............................................................................................................................85Positron  emission tom ography (P E T ) .................................................................................................................... 86Beam  line 2C and TR IM  ............................................................................................................................................ 87M icrostructures and electronics ................................................................................................................................88C Y CLO TRO N  DIVISION ................................................................................................................................................92In troduction  ....................................................................................................................................................................92Beam  p ro d u c t io n ........................................................................................................................................................... 94Cyclotron ..........................................................................................................................................................................96C yclotron developm ent ........................................................................................................................................96rf  operation  ............................................................................................................................................................101Inflector and correction plates ........................................................................................................................ 102E xtrac tion  s y s te m s ..............................................................................................................................................102Vacuum  ...................................................................................................................................................................102M ain m agnet power supplies ...........................................................................................................................102Elevating system  ..................................................................................................................................................102Ion sources and injection system  ...........................................................................................................................103P rim ary  beam  lines .................................................................................................................................................... 104Control s y s te m ............................................................................................................................................... 205Pro jects ........................................................................................................................................................................ ..A lternative ex traction  system  ................................................................................................................... 207500 f iA  upgrade ............................................................................................................................................... 20830 MeV cyclotron ......................................................................................................................................... 209O perational services ................................................................................................................. 209EX PER IM EN TA L FACILITIES DIVISION .............................................................................................................223Introduction  ................................................................................................................................................  213E xperim ental support ................................................................................................................. 214Nucleonics and IAC ................................................................................................................................. 214D ata  acquisition software ................................................................................................................. 215D etector f a c i l i ty .....................................................................................................  216M W PC  fa c i l i ty  ’ ’ ’ ’ ’ ’ "  ’ ”  ’ ' ’ ’ ' '  ’ ’ ' ’  ^ ' '  ‘ ‘ ' '  ‘ ‘ ' ‘ 1 1 7Meson hall ....................................................................................................................................... 217M9 channel ..................................................................................................................................... 217M9 channel upgrade ............................................................................................................................... 217M il  channel ................................................................................................................................... 218QQD spectrom eter ..................................................................................................................................... 218M15 channel ............................................................................................................................................... 220/zSR facility ....................................................................................................................................... 220Beam  line IB  ................................................................................................................................. 221P ro ton  hall ..........................................................................................................................................  221Beam  line 4B ................................................................................................................................. 221M R S   122A segm ented high-pressure gas cell for (n ,p ) for charge exchange experim ents ___ 123t i s o l ........................................................................................................................................................ ; ; ; ; ; 124D ual arm  spectrom eter system /second arm  spectrom eter .............................................................  225Targets ..................................................................................................................................... 227Experim ental facilities engineering ...................................................................................  228A C C ELER A TO R  RESEA RCH  DIVISION ...............................................................................................................In troduction  ...........................................................................................................  232Beam developm ent ................................................................................................................. 233C yclotron .............................................................................................................  233P rim ary  beam  lines ............................................................................................................... 237Secondary channels ................................................................................................................. 238Beam line diagnostics ........................................................................................................... 239C om puting services ............................................................................................................................... 240KAON factory ................................................................................................................................. 241TEC H N O LO G Y  AND ADM IN ISTRA TIO N  DIVISION .................................................................................... 150In troduction  ................................................................................................................................... 250Site services ................................................................................................................................... 251Safety program  ....................................................................................................................... 252Building program  ............................................................................................................................... 252Design Office ............................................................................................................................. 252M achine Shop ............................................................................................................................... 252P la n n in g ................................................................................................................................................................ ..Controls, electronics and com puting .......................................................................................  253D a ta  Analysis C entre .......................................................................................................................  256A dm inistra tion  ................................................................................................................................... 257I XA ccounting ............................................................................................................................................................ 157A dm inistrative d a ta  processing ...................................................................................................................... 157M aterials m anagem ent ...................................................................................................................................... 158Personnel ................................................................................................................................................................ 158C O N FER EN C ES, W O R K SH O PS AND M EETIN G S ......................................................................................... 159ORGANIZATION ..............................................................................................................................................................161A PPEN D IC ESA. Publications .................   164B. Users group ..............................................................................................................................................................172C. Experim ent proposals .......................................................................................................................................... 175xINTRODUCTIONBy the best indicators 1987 was a  good year for TR IU M F and its science. A lthough the num ber of employed staff and  the funding was exactly the same as for 1986 there was grow th in the num ber of exper­im ents perform ed, the num ber of users partic ipating  in experim ents, the  num ber of new proposals for ex­perim ents, the  delivery of beam  to experim ents, the num ber of papers published, the  length of th is annual report and, probably, the  num ber of m em bers of the public who toured  T R IU M F and the coverage of TR I- U M F’s program  by the various m edia. M ost of the brief accounts of research progress in this report speak for them selves and the reader is encouraged to  browse.T he various activities of T R IU M F, as described in th is report, are in tended to  convey how the project fulfills its  national purpose. T his purpose has evolved. A lthough the  purpose does not appear to  be concisely articu la ted  anywhere it probably  includes all of the following:•  to  serve as a high-profile laboratory  in fundam ental subatom ic science constitu ting  C an ad a’s contribution to  the world network of large accelerator facilities and aiming to  achieve, in th is field, the highest in terna­tional s tandards of excellence• to  provide, in subatom ic physics, a program  of na tional significance easily accessible to  scientists from  across the nation• to  a ttra c t people and ideas of the highest quality from  abroad• to  offer substan tia l opportun ities to  g raduate  s tu ­dent train ing• to  act as a catalyst for high technology enterprises w ith appropriate technology transfer program sM any experim ents a t T R IU M F in 1987 carry on the trad itio n  which has placed the project on the world m ap of subatom ic science over the past decade. The new work includes a significant leap forward in the search for transition  of m uonium  to antim uonium . This experim ent addresses the “sense of fam ily” among n a tu re ’s basic building blocks -  the quarks and leptons -  in enquiring how readily particles change into an­tiparticles. Next, the  charge-exchange facility in TR I- U M F’s p ro ton  hall now pours out im portan t publica­tions on how the quarks inside a neutron or proton flip over when a neutron or proton in teracts w ith a nucleus. T R IU M F ’s muon beam s have become im portan t tools for probing the properties of high-tem perature super­conductors and, generally, of m agnetism  in condensed m atter.Spin-offs a t T R IU M F now abound. T he isotope pro­duction facility is doubling its  sales annually. The trea tm en t of deep-seated tum ours w ith pions made great progress in 1987 and is approaching a stage at which national clinical tria ls for specific sites appear to  lie ju s t ahead.T he T R IU M F cyclotron produced much beam  in 1987 in spite of two m ajor “hiccups” in its perfor­mance. T he m ain rf transform er burned out in August necessitating a repair of more th an  a m onth; the twelve jacks which lift the  entire upper ha lf of the  cyclotron m anifested a m ajor bearing problem  which pointed to ­ward their m ajor overhaul in 1988. T he cyclotron is a very large and sensitive machine. Both the high qual­ity of its norm al operation and the strong response to m ishaps are a credit to  the  operations and m aintenance personnel of Cyclotron Division.Perhaps the  greatest continuing source of excite­m ent a t T R IU M F in 1987 was the progress toward a KAON factory. The strong in terest and advocacy of the  provincial governm ent of B ritish Colum bia -  perhaps unparalleled in the recent annals of C anadian science -  have placed th is pro ject on the threshold of construction funding. Development of the technical as­pects o f the  KAON pro ject continued throughout the year bu t it was the political a tten tion  which the project received which moved it forward.As counterpoint to  the  main them e of KAON for T R IU M F ’s fu ture we developed in 1987 a Five-Year P lan  to  guide the pro ject in the  absence of a KAON facility. This plan, developed for the  Advisory Board on T R IU M F (A BO T) of the N ational Research Coun­cil of C anada, would see m ajor upgrade of T R IU M F ’s present beam  intensity  and o f the various secondary beam  lines. I t  would see the p ro jec t’s NRC contri­bution grow by more th an  60% in five years to  a new p lateau  which promises to  keep the project com petitive w ith the o ther meson factories of the world. Of course, the  KAON pro ject would give T R IU M F a unique fa­cility of world-leading im portance for several decades. I t now appears th a t th is  C anadian  project will re­ceive strong support from  o ther nations. The case for C anada has become especially compelling.T R IU M F has recently evolved in to  a national fa­cility, under the guidance of A BO T. T he project was originally funded, in 1968, as a regional centre of ex­cellence. However, as the field achieved m ajor break­throughs in the  1970s and 1980s the im portance of T R IU M F ’s program s increased and the num ber ofpartic ipan ts from  across C anada grew. The program  now includes m ost of C an ad a’s subatom ic physicists. Therefore, the jo in t venture which operates TR IU M F is being augm ented. Several universities have been in­vited to  jo in  in a two-stage process. T he Universite de M ontreal and the U niversity of M anitoba have be­come associate m em bers en route to  full m embership. The University of Toronto is an observer on T R IU M F ’s Board of M anagem ent. Looking a t the program  of TR IU M F it clearly has, now, a national base of par­ticipants.The T R IU M F Board of M anagem ent has undergone some substan tia l changes. Peter Larkin concludes his service to  the Board a t the  end of the year having served six years concluding w ith two years of magnif­icent chairm anship. Like the salm on, on which he is a world expert, Peter Larkin has m any m echanism s tosteer his way unerringly through m urky w aters. Alan A stbury retired from  the Board and was replaced by a prom inent engineer, Joseph Cunliffe. Karl Erdm an, who has served T R IU M F in alm ost every capacity, re­tired  and was replaced early in the year by John  W ar­ren, T R IU M F ’s first director and founding father. F i­nally, Morris Belkin was replaced by Denzil Doyle, a well-known technology transfer expert from  O ttaw a. We record, w ith great sadness, M orris B elkin’s death in December. He was very helpful and generous to  T R I­UM F over m any years and particu larly  instrum ental in establishing the Shrum  Fund for scientific exchanges w ith the W eizmann In stitu te . He offered a m emorable dinner cruise to  T R IU M F and its foreign dignitaries on his large yacht on the occasion of the  ten th  anniversary celebration in Ju ly  of 1986.2SCIENCE DIVISIONIN T R O D U C T IO NT he year 1987 was another excellent one for sci­ence a t T R IU M F. The num ber of proposals subm itted  to  T R IU M F continued to  rise and reached the record num ber of 41 for the  Decem ber m eeting of the EEC. In spite of some difficulties m ainly caused by rf prob­lems during the sum m er, the am ount of beam  delivered during the year was also a record (331 m A h). During Ju ly  we successfully ran  for the first tim e w ith average beam  curren ts of around 200 pA , double the original design goal of the  T R IU M F cyclotron, for two weeks.In particle physics the m ost notew orthy achievement was the setting  of new upper lim its for the conversion of m uonium  in to  antim uonium  by E xpt. 304. This ex­perim ent uses a radiochem ical technique which, w ith the d a ta  taken  this year, will be sensitive to  a branch­ing ra tio  for th is conversion, forbidden in the standard  model bu t allowed in some grand unified theories, of less th an  3 x 10~5. Further runs are planned in 1988 to  increase the sensitivity.M ajor pieces of equipm ent were constructed  and tested  for im portan t experim ents a t Brookhaven (BNL 787) and the SLAC linear collider (SLD). C onstruction was com pleted for BNL 787, a  B rookhaven-P rinceton- T R IU M F collaboration to  search for the decay K + —► ir+ up w ith two to  three orders of m agnitude increased sensitivity  over previous m easurem ents. D ata-taking will commence a t the  Brookhaven AGS in February 1988. M ost of the appara tus for SLD being m ade at T R IU M F is now com plete and in the process of being shipped to  SLAC.T R IU M F ’s longstanding in terest in the N - N  in ter­action a t in term ediate energies continued w ith a m ajor new experim ent (182) to  m easure A yy in n-p scatter­ing to  fu rther constrain N N  phase shifts. D ata-taking was com pleted a t four energies. P relim inary results are now coming ou t from  a m easurem ent of the ratio  R t / D t (332) which finished da ta-tak ing  in 1986.T he nuclear physics program  in the proton hall con­tinued a t a very high level, w ith twelve im portan t ex­perim ents being com pleted on the (p ,n ) (n ,p )  CHAR- G EX facility. These experim ents covered a very wide range of interest, from  searches for G T  streng th  in s-d shell nuclei such as 54Fe, to  looking for giant isovector resonances in m edium  and heavy nuclei, to  tests of shell model lifetime calculations for double b e ta  decay. T he C H A R G EX /M R S complex continued to  provideT R IU M F with facilities for doing (p , p ' ) , ( p , n ) and (n ,p )  experim ents a t in term ediate energies which are unm atched anywhere else in the world.In the meson hall the  m ain em phasis continued to  be on pion scattering  and break-up reactions on a polar­ized deuteron target. Experim ent 337 com pleted data- taking on m easurem ents of T20 and t2\ in nd  elastic scattering, while E xpt. 331 m ade m easurem ents of the polarization transfer param eters Kt„ and K ss in the 7rd —► pp reaction. A t the end of the year measure­m ents of the vector analysing power of nd  —+ pp were in progress in E xpt. 375. E lastic scattering  cross sec­tions of pions on protons (E xpt. 394) and on deuteron (E xpt. 399) were also m easured.A nother notew orthy experim ent was 327, which studied the (7r+ , 7r+ 7r~) reaction on 160 ,  28Si and 40Ca on M il .  The QQD spectrom eter was used in coinci­dence w ith a large stack of p lastic  scintillators to  detect the outgoing pions.The pSR  program  continued to  find new uses for muons as probes of m atte r. This year the em phasis was using m uons to  probe the m agnetic properties of the new high tem pera tu re  superconducting  m aterials, the discoverers of which received this y ear’s Nobel prize. Groups from  Bell Labs, U niversity of Tokyo and UBC have all been very active th roughout the year, under the general auspices of Expt. 469. The level cross­ing resonance technique continues to  find m any appli­cations ranging from  elucidating anom alous m uonium  form ation in sem iconductors (E xpt. 367) to  free radical chem istry (E xpt. 398). More trad itiona l areas of ^SR, such as high pressure /rSR in liquids (E xpt. 362) and reactions of m uonium  w ith halogen gases (Expt. 420) con tinue to  p rosper. T h e  year fin ished on  a  fine no te w ith the first observation of the  m uon spin echo phe­nomenon (E xpt. 449), which promises to  have im por­tan t applications in condensed m a tte r in the future.The Theory group continued to  play a v ital and stim ulating role in the work of the Science Division. As well as carrying ou t a w ide-ranging research pro­gram , the group is responsible for organizing our pro­gram  of short- and long-term  visitors. In teractions be­tween theory and experim ent, which are so successfully fostered by the Theory group, are essential to  the long­term  v ita lity  of the experim ental program .3The contributions on individual experiments in this report are outlines intended to demonstrate the extent o f  scientific activity at T R IU M F  during the past year. The  outlines are not publications and often contain preliminary results not intended, or not yet ready, fo r  publication. Material from these reports should not be reproduced or quoted without permission o f the authors.4P A R T IC L E  P H Y S IC SE x p e rim e n t 182S pin  co rre la tio n  p a ra m e te r  A yy in  n-p e lastic  s c a tte r in g(W.T.H. van Oers, W.D. Ramsay, Manitoba)T he purpose of th is experim ent was to  m easure the spin correlation param eter A yy in n-p  elastic scattering  to  an accuracy of ±0.03  a t 220, 325 and 425 MeV over the  angular range 50° to  150° in the centre-of-mass system . T he m easurem ent was carried out by scat­tering polarized neutrons from  polarized protons in a frozen spin ta rg e t (FST ) and determ ining the asym­m etry  w ith different n-p  spin correlations.Polarized neutrons, produced a t the LD 2 ta rget in beam  line 4A by transverse polarization transfer from polarized protons, were collim ated through the 9° port; the  spin direction was ro ta ted  to  the vertical plane by two spin precession dipoles (Bonnie and Clyde). The recoil protons were detected in proton range counters consisting of time-of-flight s ta r t and stop counters and four delay-line cham bers. The scattered  neutrons in coincidence were detected  in 105 cm x 105 cm scintil­la to r arrays. The details of the experim ental set-up can be found in the  U niversity of M anitoba In term ediate Energy Progress R eport, 1986, 1987. T he frozen spin target consisted of bu tanol beads contained in a 5 cm high, 3.5 cm wide and 2 cm thick rectangular box. In order to  reduce the m ultiple scattering  of the forward and backward scattered  protons we had two orientar tions of the target. Initially  for the  angular range of 90°-150° (c.m .) the ta rg e t was set w ith its 3.5 cm side perpendicular to  the neutron beam . For the  the rest of the angular range (50°-90° c.m .) the target was ro­ta ted  by 90° so th a t 3.5 cm side was along the beam  direction.In order to  select n-p  elastic events from  n-np  back­ground we have form ed four kinem atic constraints, viz.:(1) Energy sum: Tp + Tn(2) Transverse m om entum  sum:Pp sinOp cos<t>p +  Pn sin0„ cos<f>n(3) O pening angle: 9P + 6n(4) C oplanarity: <j>p + <j>nIn calculating the opening angle the  deflection of protons in the FS T  m agnetic holding field is taken into account. By knowing the flux norm alized left (L ) and right (R ) counts one can then ex trac t the spin correla­tion param eter A yy as follows:a  -  1 t * - 1* m”  PB P r ( X  + l )whereX 2 — (L++ + ^ — )(-ft++ +  &— ) r<)\(£ + _  +  L _ + )(R + _ +  R _ + )Pb  and Pp  are the beam  and ta rg e t polarizations, re­spectively. T he subscripts, + + ,H — , — h ,— , are four different com binations of beam  (first index) and target (second index) spin orientations.T he m axim um  target polarization  obtained during the run was 82% w ith a m axim um  decay tim e of 765 h. T he ta rg e t polarization as m easured by an NM R sys­tem  is known to  no b e tte r th an  4%, however, the present experim ent required th a t it should be known to an absolute accuracy of 2%. W ith  th is in m ind we have perform ed an independent calibration of the NM R sys­tem  using unpolarized protons a t the  beginning and end of each d a ta  taking run. An unpolarized beam  of 500 MeV protons im pinged on a stack of graphite and produced protons by elastic scattering . T he protons scattered  a t 9° passed through the neutron collimator and a superconducting solenoid (Superm an), which ro­ta ted  the unw anted polarization of the  secondary beam  by 90°. T he protons scattered  from  the FS T  were de­tected in pro ton  range counters set a t 24°. The recoil protons were detected in the central region of the big scintillator arrays set a t 61°. Note th a t a t this an­gle and energy the p-p analysing power is very accu­rately known [Greeniaus et al., Nucl. Instrum . M ethods A 3 2 2 , 308 (1979)]. T hus by m easuring the asymme­try  and knowing the analysing power we m easured the target polarization  to  the required accuracy.T he prelim inary d a ta  for A yy a t 325 and 220 MeV are p lo tted  in Fig. 1. The predicted values from  differ­ent phase-shift analyses and nucleon-nucleon potentials are also shown. We also ex trac ted  the analysing pow­ers over the  same angular range a t all three energies.E x p e r im e n t 248 A  s tu d y  o f  th e  d ec ay  tt —*■ ev  (T. Numao, TRIUMF)T he m ain goal of the  present experim ent is to  im­prove the m easurem ent accuracy of the branching ratio R  =  (7r —* e v ) / ( i r —► p v)  by a factor of three in order to  provide a m ore stringent test of universality of weak interactions for different generations.The data-tak ing  was com pleted in 1986 and about 3 x 1057r —► ev  decay and 2 x 108 n-v-e  chain decay events were recorded. Extensive analyses have been done in the areas of system atic d a ta  calibration, scan­ning full d a ta  sets and M onte C arlo sim ulations.5Angle (c .m .)b )Angle (c .m .)Fig. 1. (a) A yy a t 325 MeV, (b) A yy a t 220 MeV.A background-suppressed 7r —» ev  spectrum  has been exam ined for evidence of massive neutrinos [Azuelos et al., Phys. Rev. L ett. 56, 2241 (1986)] and other exotic particles [Picciotto et al., Phys. Rev. D, in press], A signal of the  decay 7r —+ e v M , where M  is a m ajoron or o ther neu tral boson escaping the detec­tor system  w ithout any interactions, was sought in the 7r —► ev  spectrum . Upper lim its of the branching ra­tio  (90% C.L.) were obtained for hypothetical bosons in the m ass region 0-130 M eV /c2 and are shown in Fig. 2. T he decay ir —* e v v v  was also sought in the sam e spectrum  and an upper lim it 3.5 x 10-6  was ob­tained.E x p e r im e n t  249R a d ia tiv e  m u o n  c a p tu r e  w ith  th e  T P C( G. Azuelos, TRIUMF)R adiative m uon capture (RM C) is a weak semilep- tonic process which is particu larly  sensitive to  the in­duced pseudoscalar form  factor gp o f  the  hadronic cur­rent. T his experim ent is to  m easure RM C on light nu­clei to  investigate its possible renorm alization in the nucleus, and is a precursor to  a m easurem ent of RMC on hydrogen (E xpt. 452). T he experim ent has been described previously (1986 annual report, p. 8); data-Fig. 2. Branching ratio  lim its for r  —► e v M  process vs. mass of the M  particle.taking was com pleted in May. M easurem ents have been m ade of RM C on calcium , oxygen and carbon; the photon energy spectra  ob tained w ith a 1.0 m m  thick Pb converter are shown in Fig. 3. Only the region of the spectrum  above about 57 MeV is usable, due to  the unavoidable background for brem sstrahlung of Michel electrons. D a ta  have also been obtained on the various backgrounds (pion-induced, cosmic-ray, muon- decay brem sstrahlung) and contributions to  the  final system atic error. D ata  analysis is well under way, in­cluding a full M onte Carlo of the  experim ent based on the CERN program  G EA N T. T he s ta tis tica l error on the RM C ra te  for each nucleus is less th an  5%; the final system atic error is expected to  be less th an  10%.E x p e r im e n t  287M e a s u re m e n t o f  p a r i ty  v io la t io n  in  p-p  s c a t te r in g  (J. Birchall, W.T.H. van Oers, Manitoba; G. Roy, Alberta)The parity-violating longitudinal analysing power A z arises from  the interference of opposite parity  am ­plitudes in p-p scattering . In general, A z (9) is ex­pressed as a linear com bination of parity-m ixed partia l wave am plitudes: [(1S0-3F>o), ^ T Y 1^ ) ,  C ^ V 3-^ )  • • •] in order of increasing angular m om entum , where the angular d istribu tion  of each term  is governed by the strong in teraction . T he relative strengths of each term  are determ ined by m atrix  elem ents of the weak me­son exchange in teraction  and m ust be calculated using appropriate wave functions. T he weak meson-nucleon couplings hpp and h^f  con tribu te  to  the  lowest-order (1P0-3Po) te rm  w ith approxim ately equal weight. In contrast, the  (3 P 2 -1 D'l) which contributes significantly to  A z above 100 MeV is alm ost entirely  due to  weak p exchange [Simonius, A IP Conf. P roc. 150  (AIP, New York, 1986), p. 185 and private com m unication].M easurem ents of A z a t 15 and  45 MeV [Kistryn et al., Phys. Rev. L ett. 58 , 1616 (1987) and references therein] have established the lowest partia l wave con­tribu tion  as (1 .5 ± 0 .2 )x l0 - 7 . To date  no interm ediate-Gamma Ray Energy (MeV)Gamma Ray Energy (MeV)Fig. 3. Photon energy spectra from RMC on calcium, carbon and oxygen.energy experim ent has been perform ed, and the higher partia l wave contributions are undeterm ined. A unique s itua tion  exists a t 230 MeV, where the contribution of the lowest partia l wave vanishes [Simonius, op. cit.] in the expression for A z . T his is purely a strong in ter­action effect; the angular d istribu tion  of the ( 15 o-3i ’o) term  in tegrates to  zero from  0 to  90° in the centre ofm ass a t 230 MeV, w ith no dependence on the values of the weak meson-nucleon coupling strengths. To an ex­cellent approxim ation a t th is energy, the  longitudinal analysing power in p-p scattering  m easures the  (3P 2- l D 2) te rm  alone, which in tu rn  is dom inated entirely by the p exchange contribution. Thus, a m easurem ent of parity  violation in p-p sca ttering  a t 230 MeV affords a unique opportun ity  to  m easure hpp .An angular d istribu tion  m easurem ent was originally considered preferable from  an experim ental standpoint due to  the extrem ely sm all predicted value [Simonius, op. cit.] of the to ta l asym m etry A z ~  4 x 10~8, which resulted from  the vanishing of the  ( 1S’0-3Po) contribu­tion. A t the Sym posium /W orkshop on P arity  Viola­tion in Hadronic Systems held a t TR IU M F in May it was determ ined th a t an ou tdated  value of the anom a­lous isovector m om ent used in the  calculation had re­sulted in a factor of two underestim ate  of A z . Thus, a m easurem ent of A z a t 230 MeV to a precision of ± 2  x 10 - 8 , as has been achieved a t lower energy, will provide a significant constrain t on the weak p-nucleon coupling.To determ ine the parity-violating analysing power A z a beam  of longitudinally polarized protons a t 230 MeV will be scattered  from  a liquid hydrogen target, and the helicity dependence of the  to ta l elastic sca tter­ing cross section will be m easured. T he longitudinal analysing power can be m easured in two ways: by col­lecting the forw ard scattered  protons in a large solid angle detector and norm alizing the scattering signal to the  incident beam  flux, and by m easuring the beam  current to  high precision before and after the  liquid hydrogen target.T he P P IC  noise tests discussed in last year’s progress report indicated  th a t it  is possible to  mea­sure A z by both  the  scattering  and the transm ission m ethods sim ultaneously, to  com parable sta tistica l ac­curacy. Excluding the tim e required to  perform  control and calibration  m easurem ents, the required statistical accuracy of ± 2  x 10~8 can be achieved by both  m eth­ods in approxim ately 200 h of running tim e a t 500 nA, Pz — 0.8. Since the system atic errors in the two cases are very different, a com parison of the  scattering  and transm ission m ethods will provide a unique and invalu­able check on the experim ental results.In last year’s progress repo rt we reported  tests of a beam  position servo system  which was able to  hold the beam  position fixed a t a given location. In October this year we tested  a double loop system  to hold the beam  position fixed a t two locations simultaneously. We also tested  a new higher curren t amplifier for the m agnetic beam  deflection system .A pro to type scattering  detector is shown in Fig. 4.It is a p lanar ionization cham ber filled w ith hydrogen7iFig. 4. Prelim inary design of a prototype ionization cham­ber scattering detector. Beam enters from the left.gas a t a pressure of 1 a tm . There is a central high voltage plane, in fron t and behind which is a sym m etric arrangem ent of sense planes a t ground po ten tia l to  col­lect the  charge released by protons travelling through the hydrogen gas. T he back plane is m ounted on a rigid back plate. T he prim ary  proton beam  passes through a central hole in the cham ber so as to  avoid heating of the  gas and  scattering  of protons from  entrance and exit windows.T he m ost im p o rtan t system atic error in the m ea­surem ent of the  parity-violating analysing power is due to  the beam  polarization no t being entirely parallel to its m om entum . T his is because an error is induced which is propro tional to  the first m om ent of transverse beam  polarization. It is therefore essential to  be able to m easure the d istribu tion  of the transverse com ponents of polarization across the beam  profile.A pro to type design of a polarim eter to  do th is is il­lustra ted  in Fig. 5. T he polarim eter contains a carbon blade which is scanned across the  beam . As the ver­tical blade moves across the  beam  two detectors (left, right) count the  protons scattered  from  the blade. The left-right sca ttering  asym m etry  m easures the  vertical com ponent of polarization  of th a t p a rt of the beam  in­tercep ted  by the  rod. A fter a horizontal scan the blade is ro ta ted  by 90° and is scanned up-down through the beam . A pair of up-down detectors then  measures hor­izontal com ponents of beam  polarization. A novel fea­tu re  of th is design is th a t the up-down and left-right de­tectors move w ith the blade. T his reduces system aticFig. 5. Sketch of the scanning polarim eter. The carbon blade is shown in the vertical position. The scattering de­tectors are contained in the ring downstream  of the blade.errors in the m easurem ent of transverse polarization by two orders of m agnitude.E x p e r im e n t  304M u o n iu m -a n tim u o n iu m  c o n v e rs io n  (A. Olin, TRIUMF/Victoria)T his experim ent is a search for p,+ e~ —+ /r~e+ , a re­action forbidden by lepton num ber conservation. This process can arise na tu ra lly  in theories w ith  M ajorana neutrinos, especially if the  neutrino  masses are pro­duced via a coupling to  a new lepton num ber violating Higgs particle.The experim ental set-up is shown in Fig. 6 . Muons from  M15 are m oderated  and stop near the  back of a 10 m g /cm 2 th ick layer of SiC>2 powder w ith 7 nm  par­ticle diam eter. T he therm alized m uonium  (M u) atom s diffuse from  the  powder across a 2 cm vacuum  gap to a 50 nm  W O 3 layer evaporated  onto a Mo foil. Con­verted fi~ then  cap ture  on W  atom s to  produce 184Ta. A pproxim ately 50% of the  recoiling T a atom s rem ain in the foil, which is removed from  the vacuum  system  after a 12 h exposure. In order to  prevent the  form ation of a surface layer on the W O 3 the  evaporation is done in an antecham ber, and then im m ediately introduced into the UHV cham ber near the  SiC>2. T his cham ber was m aintained a t a pressure of ~ 1 0 ~ 8. Three layers of m agnetic shielding were used to  reduce the m agnetic field seen by the Mu to  <10 mG.8y prompti. 1 i i i i I i i i i IUHV RoughingFig. 6 . Vacuum system for the muonium exposures.( 0 - 7 > {M X350 400 450 500 550 350 400 450 500 550KEV KEV^prom pt Tdelayed ’7/ )prom pt’7/delayed350 400 450 500 550 350 400 450 500 550KEV KEV7 prompt ^delayed ( ^ ’7/ )prompt’7/delayedi350  400  450  500  550  350  400  450  500  550KEV KEVFig. 7. Spectrum  after counting a 0.45 m g/cm 2 W O 3 sur­face in which 130,000 n~  had been stopped. The 414 keV gam ma is characteristic of 184Ta. The effects of the var­ious coincidence requirem ents on signal and backgrounds are shown.KEV KEVFig. 8. Spectrum  of WO3 surface exposed to muonium for 10 h.9T he efficiency of our appara tu s for detecting p~  has been m easured experim entally  by exposing W O 3 sam ­ples to  a  carefully m easured flux of stopping p~  and detecting the resulting 184T a in our low-level counting appara tus. We show in Fig. 7 results for a 450 p g /c m 2 ta rget in which 130,000 fi~ had  been stopped. The effect of the various requirem ents on both  signal and backgrounds are clearly seen, and the rates observed confirm our initial estim ate  of the relevant p + -capture yields. Background count rates have been m easured by exposing 12 p  W  foils to  a p + beam . From this test we expect a background 414 keV count every 100 shifts. The count ra te  from  n a tu ra l radioactiv ity  in the detector and shielding is less th an  1 count/40  shifts.T he emission of m uonium  from  silica powder was studied in an earlier run  by stopping a beam  of muons in a 13 m g /cm 2 powder layer inclined at 60° to  the beam  direction. T he stopping d istribu tion  in the pow­der was varied by adjusting the beam  m om entum , and the yields into the vacuum  were m easured. The re­sults were incom patible w ith a simple diffusion model for the  m uonium . However, a model where the muo­nium  escapes from  an agglom erate w ith an exponential tim e d istribu tion , and then  diffuses between the grains, seems to  give a  good account of the vacuum  yields, allowing ex trapo lation  to  different stopping distribu­tions.Surface monolayers depositing on the W O 3 surface could prevent the therm al m uonium  from  reaching the W  atom s. We have studied  the ra te  of accretion of m onolayers on these surfaces a t SFU using X-ray pho­toelectron and Auger electron spectroscopy techniques. T he thickness of the surface layers was estim ated  from the streng th  of the  carbon signal and the attenuation  of the  tungsten  line. On the  basis of th is m easurem ent we calculate th a t  in 12 h a t a pressure of lx lO -8  10% of a  monolayer will be deposited. In our appara tus we have achieved a vacuum  of 2 x l 0~ 9, b u t typical opera­tion  has been a t lx lO - 8 .We have com pleted 12 successful 12 h exposures of W 0 3 -coated foils. Figure 8 shows results of counting a ta rget exposed for 12 h for evidence of 184Ta. Based on these exposures we expect th a t  th is m easurem ent was sensitive tor(/z+ e —► p e+ ) T(p  —> evv)< 3 x 10-Further runs are planned to  increase the sensitivity and to  explore fu rther the  vacuum  m uonium  mechanism.E x p e rim en t 332R a tio  o f  sp in  tra n s fe r  p a ra m e te rs  D t/R t  in  d(p,n)pp q uasie lastic  s c a tte r in g(C.A. Davis, Manitoba)T he ra tio  of W olfenstein spin transfer coefficients dt (vertical-to-vertical spin transfer) and rt (sideways-to- sideways spin transfer) in quasielastic scattering from deuterium  d(p, n)pp  has been m easured a t four energies a t 9n =  9° (lab). As the ra tio  can be determ ined in a m anner which is independent of the analysing powers of the polarim eters for m easuring the  polarizations of the protons and neutrons, overall system atic norm al­ization errors are elim inated.The analysis of th is experim ent has been completed and the results are given in Table I. T he ra tio  D t /R t  for free np  sca ttering  has been corrected for deuteron D  s ta te  and final-state in teractions. D t / R t p lo tted  as a function of energy and com pared to  several present- day phase-shift predictions is presented in Fig. 9.P u ttin g  these results into the  C200, C300, C400 and C500 phase-shift solutions of A rn d t’s SAID program , we can make the following sta tem ents: T he values of e 1 and €3 are reduced, ej being com paratively flat (~ 4 °) over the  200-500 MeV region. 3S'i, 3D \ ,  3 £>2 and es­pecially 1P’i are all affected, the rough area aroundTable I. Results for quasielastic dt/ r t and deduced D t/R t ,  where the final errors in D t/ R t  also include an error due to  uncertainty in knowledge of the ATn cut. The results have been corrected for target background.Tp(MeV)W  (c.m.) (MeV)0„(c.m .)(deg)dt/rt(v a lu e )± (s ta t.)i(sy s .)D t/R t222.7 1986.2 160.98 0.0144±0.0064i0.0033 -0 .0190 i0 .0072324.1 2033.6 160.54 -0 .1 9 1 6 i0 .0 0 4 6 i0 .0 0 3 2 —0.2328i0.0057424.8 2079.6 160.11 -0.3380±0.0045±0.0050 —0.3731±0.0068492.1 2109.8 159.82 —0.4391±0.0085±0.0060 — 0.4892i0.010710Deduced free np from d(p,n)pp al 9 deg. n Lab. AngleEnergy  (MeV)Fig. 9. The ratio  D t / R t ■ Our d a ta  (solid squares) are compared to  the phase-shift predictions of A rndt (SM87, solid line), the Saclay phase shifts (in two energy regions, dash lines), and the BASQUE phase shifts (dot-dash line), all derived from SAID.300 MeV tending to  be sm oothed out. There are, how­ever, large correlations, especially C(e\ x  £3). We hope to  reduce these correlations and fu rther improve the phase shifts by addition of our A nn and P  d a ta  which are being analysed now (see E xpt. 182, p. 5).E x p e r im e n t  369T e s t o f  c h a rg e  s y m m e try  in  n-p e la s t ic  s c a t te r in g  a t  350 M eV(W .T .H . van Oers, Manitoba; L.G. Greeniaus, TRIUMF)An experim ent sim ilar in m ost respects to  our re­cently com pleted T R IU M F E xpt. 121 is being prepared for da ta-tak ing  in the  w inter of 1988-1989. The exper­im ent will m easure the  difference in analysing powers A n and A p (where the subscrip t denotes the polar­ized nucleon) in neutron-proton elastic scattering  at 350 MeV. Designed as a null m easurem ent, the exper­im ent will achieve an accuracy in A  A  — A„ — A p of ±0.0008 (or ±0.026° in the zero-crossing angle.O ur m easurem ent of A A  a t the zero-crossing angle a t an incident neutron  energy of 477 MeV has yielded A A  =  (37 ±  17 ±  8) x 10- 4 . This result should be com pared to  the range of values from  the m ost recent theoretical calculations of (21-74) x l0 ~ 4. These calcu­lations include (collectively) estim ates of contributions from  direct electrom agnetic effects, the neutron-proton m ass difference in one-pion and p exchanges, and the isospin m ixing p°-u> meson exchange. Some other sm aller effects have also been evaluated. A lthoughthe various predictions are sim ilar in m agnitude, they differ significantly in their detailed predictions. The Iqbal, T haler and W oloshyn (IT W ) calculation [Phys. Rev. C 36, 2442 (1987)] is substan tia lly  lower than  those by Miller, Thom as and W illiam s (M TW ) [Phys. Rev. L ett. 56, 2567 (1986); Univ. of Adelaide preprint A D P-87-21/T40], Ge and Svenne (GS) [Phys. Rev. C 34, 756 (1987)] or Holzenkamp, Holinde and Thom as (HHT) [Univ. of Adelaide p reprin t A DP-87-21/T38]. HHT also predict a different energy dependence than  the o ther calculations. T he differences between the theoretical predictions are the  source of much discus­sion. In Fig. 10 the M TW , H H T and GS predictions a t 350 MeV are com pared. T he electrom agnetic term  accounts for much of the M W T -G S difference. The M T W -H H T  difference is due to  the trea tm en t of the p and p°-ui term s. CSB experim ents sensitive to  the region away from  the cross-over angle can possibly dis­tinguish these la tte r term s and m ay be able to  make a stringent test concerning the meson exchange picture of the N N  in teraction  a t short distances.T he 350 MeV m easurem ent will be perform ed in the m anner of the recently  com pleted E xpt. 121. R ather th an  m easuring the asym m etry difference directly, the angles a t which the asym m etry crosses through zero will be determ ined. T his difference between the zero- crossing angles is directly proportional to  the difference in asym m etries a t th a t angle. Using th is technique we perform  a null m easurem ent where the m ajority  of pos­sible system atic errors cancel because the A„ and A p m easurem ents are m ade w ith exactly the  same physical apparatus. T he only changes are to  the polarizations on the beam  and target.o >o to »0 »0 ISO 110Angle (cm)Fig. 10. Comparison of the A A  angular distribution from M TW , GS and HHT. Differences are described in the text. The arrow shows the point where the analysing power crosses through zero. The angular range of the experiment is also shown.11T he solid angle for th is experim ent will be consider­ably larger th an  for E xpt. 121. T his will allow us to choose an angle region th a t  is asym m etric about the cross-over angle and to  a ttem p t a m easurem ent where the in teresting p°-u> te rm  is relatively large.T he new experim ent is essentially identical to  the successfully com pleted pro ject a t 477 MeV. The m ajor differences com pared to  E xpt. 121 are:1) Larger solid angle —  increased event ra te  w ith only a m arginal loss in discrim ination against back­ground. Trigger ra te  due to  (n , np) events will increase. We have recently ex trac ted  the angular d istribu tion  of the charge sym m etry breaking effect in the  477 MeV da ta . W ith  the increased precision and larger angle range we should be able to  distinguish the presence of the  p°-u) m ixing term  a t a level of about ±0.0015 in a bin of a few degrees.2) Wedge degrader removed —  increased trigger ra te  due to  (n ,n p ) events which will be elim inated off line. Some analysis problem s will be elim inated. Fewer n- p  elastic events will be lost due to  reactions in the degrader.3) FST  volume reduced to  35 cm3 and a rectangu­lar shape used. This m aintains the energy loss and m ultiple sca ttering  of the protons a t the values of the previous experim ent.4) T he neutron  beam  will have higher intensity  and polarization. T he la tte r reduces the tim e required to  achieve a given precision and makes the two aspects of the experim ent m ore sim ilar.5) T he system  will allow a secondary target to  be viewed for control purposes and background checks.6) Incorporation  of front-end intelligence —  elimina­tion  of (n ,np ) background due to  the high anticipated  trigger ra te . T h is will necessitate a J 11 processor in the CAM AC branch. T his is a result of our desire to  increase the solid angle even m ore th an  in E xpt. 121.M easu rem en t o f  K + —*■ x+ vvB N L  787 ( B N L -P r in c e to n -T R IU M F  c o lla b o ra t io n )(D. Bryman, TRIU M F/Victoria)The decay K + —*■ tt+ X °  (where is one or more light, neu tral, weakly in teracting  particles) will be searched for a t the level < 2  x lO -10  in E xpt. 787 a t Brookhaven N ational Laboratory  by a collabora­tion  from  BNL, Princeton  U niversity and TR IU M F. K + —*■ 7r+ v v  offers a unique testing ground for higher- order weak effects in the  stan d ard  model not dom i­nated  by long-distance effects. Recent observations of bb m ixing could im ply a branching ra tio  as high as 10-9  for K + —*■ ir+vv  due to  large mixing angles and a high m ass for the top quark. O bservation of a signal in th is region would serve to  validate the standard  modelw ith three generations and place severe constrain ts on its param eters.T he observation of an  apparen t K + —► tt+vV sig­nal above 10-9  would serve as a d ram atic  indicator of the presence of new physics. T he least exotic pos­sibility is the occurrence of add itional generations of neutrinos. O ther possibilities include the production of the  supersym m etric partners of the  photon, gravi­ton and the Higgs. In some versions of supersym m e­try  the decay K + —► 7r+ 7 7  could occur a t almost the current experim ental lim it for K + —+ ir+uV which is 1.4 x 10- 7 . Any proposed in teraction  which induces neu tral flavour-changing processes (e.g. technicolour) will also contribute to  the K + —► tt+vv  ra te . Conse­quently, a large window for possible new physics exists.T he experim ent will also be sensitive to  o ther in­teresting decays such as K + —+ 7r+ 7 7 , K + —> pe, K + —► 7r+ e+ e~, K + —» 7r+ /r+ /i~ , K + —>■ p +vvV,  K + —*• e+ 1/7 .Figure 11 shows the appara tus which is nearing com­pletion. The detector is designed to  have a large geo­m etrical acceptance (27r sr) for the  K + —► n + vV  decay mode while m axim izing the rejection of background processes such as I<+ —* p +v  ( K ^ ) ,  K + —* p +v y  and K + —*• 7T+ 7r° ( K v 2) and others. Sensitivity  for iden­tification of unaccom panied pions from  K + —*■ tt+ vV is accomplished through m easurem ent of m om entum , kinetic energy, range, decay sequence 7r —* p  —* e, and efficient rejection of b o th  single photons and photons from  7r° decay.T he 800 M eV /c K + beam  is b rought to  rest in a 10 cm  diam eter ta rg e t consisting of groupings of scin­tillating  fibres 2 m m  in d iam eter. T he decay pions pass through a cylindrical d rift cham ber which m ea­sures their m om enta in the 1 T  m agnetic field w ith resolution a&p < 2%. T he pions then  stop in a plastic scintillator range stack which also contains M W PCs. Each range stack counter is viewed from  bo th  ends by 2 in. pho to tubes read ou t by transien t digitizers. The digitizers record a com plete history  of scintillator light o u tp u t as a function of tim e. T he to ta l energy of the decay pions will be m easured by sum m ing the pulse heights of the ta rg e t and range array  elem ents w ith an anticipated  resolution <re ~  3%.The detector is com pletely surrounded by a  P b  scin­tilla to r gam m a veto. M onte C arlo calculation of pho­ton detection  inefficiencies for the  proposed configura­tion found an overall 7r° inefficiency 5 x 10-6  in the energy range of interest. T he efficiency is lim ited by photonuclear absorption.A branching ra tio  sensitiv ity  B ( K + —*■ n+vv)  <  2 x 10“ 10 will be achieved in a run  of 2500 h w ith a stopping ra te  of 3 x 105/p u lse  a t the  AGS. D etailed estim ates based on m easurem ents a t BNL and TRI-12Fig. 1 1 . Experim ent 787 detector.UM F and M onte C arlo calculations indicate th a t <1 background event is to  be expected. Lim its possible on the process K + —+ 7r+ a would be in the region < 1 0 ~ 10.A week-long test run  occurred in May, w ith 25% of the detector instrum ented . The lim ited conclusions draw n from  th is effort supported  critical estim ates of counting rates and background rejection capabilities.In the  following progress is described on some of the principal activities of the T R IU M F group: central drift cham ber, endcap photon veto, gallium  arsenide tran ­sient recorders, beam  counters and cham bers, d a ta  ac­quisition and trigger system s, and analysis and M onte Carlo software.T he central drift cham ber system  was developed a t T R IU M F and was shipped to  BNL in A ugust. The active volume is enclosed by Al endplates and graphite- epoxy cylindrical walls. T he cham ber is arranged in five layers of m ultiple sense-wire cells. Three layers are axial and two are a t a stereo angle of 3.5°. The wires are staggered by 500 ^m  from  the cell axis to  provide local resolution of the  left-right ambiguity. Six central sense wires are used, resulting in up to  30 points m easured on a track . The half-w idths of the cells are 1 cm for layers 1 and 2 and 1.5 cm for layers 3, 4 and 5. There are no poten tia l wires adjacent to  or between the sense wires. C rosstalk between sense wires after com pensation is <5%  and electrostatic  deflection at the m iddle of the wire will be <40 [im. The Lorentz angle of d rift is 25° for a m agnetic field of 1 T . Sinceonly the central six wires are used, there is no loss of efficiency and a good distance vs. tim e relationship is m aintained throughout.The wires are tensioned between 0.95 cm thick Al endplates spaced by 50 cm between 0.51 mm thick cylinders. T he inner cylinder is 80 m g /cm 2 graph ite /epoxy  rigidly attached  to  the endplates. The outer cylinder was installed w ith an O-ring gas seal after the  cham ber wires had  been strung. The end­plates were prestressed according to  calculations to m aintain  uniform  wire tension. T he sense wires are positioned by precision grooves in a  molded Vespel feedthrough. Each injection-m olded feedthrough is epoxied in a precision-m achined slot in the  endcap and carries a finger stock p rin ted  circuit board  for gluing and soldering the tensioned wires. T he electronics for each sense wire, designed and constructed  a t TRIU M F, consists of an on-board low power (24 m W ) hybrid pream plifier w ith o u tp u t tran sm itted  to  an amplifier- discrim inator a t a distance of approxim ately 35 m from the cham ber. The T D C s purchased were the LRS 1879, 500 MHz Pipeline T D C . T he m easured rm s resolution from  the electronics system  is approxim ately ~  1 ns, resulting in a 50 f im  uncerta in ty  for the argon /ethane gas w ith drift velocity v<i — 5 cm //rs.Single-cell and  m ultiple-cell p ro to type chambers were constructed  and tested  extensively under re­alistic conditions including m agnetic fields and the main cham ber was extensively tested  a t TR IU M F with13cosmic-rays. Local position resolution of cr —150 /im  was obtained. Track-fitting of d a ta  from  200 M eV /c pions from  the M i l  beam  a t TR IU M F gave position resolution consistent w ith <  2% m om entum  resolution for the  787 cham ber.Two endcap photon  detectors surround the beam  upstream  and dow nstream  of the  stopping target, each covering abou t 20% of the  47T solid angle. The require­m ents are very good efficiency down to  1 MeV visible energy and high ra te  capability  in a 1 T  axial m agnetic field. These dem ands were m et by building a highly segm ented detector using a lead scintillator sandwich assembly read out via very fast wavelength shifter bars.Each endcap detector consists of 24 wedge modules arranged to  form  a cylinder around the beam  pipe from an inner radius of 10 cm to  an outer radius of 40 cm. Each m odule is m ade up of 66 layers of lead “peta ls” (1 m m  thick) and  scin tillator (5 m m  thick). The scin­tilla to r petals are coupled via a 0.3 m m  air gap to  a BB O T waveshifter bar which re-em its light in the wave length region of 430 nm  corresponding to  the  peak of bialkali pno tocathode sensitivity. T he shifted light is piped outside the  m agnet yoke to  2 in. phototubes (EM I 9954) via 1.5 m  acrylic rods. C ritical to  the op­eration of the  endcap is the m atching of the scintilla­to r light emission spectrum  to  the  wave length shifter absorption  band. Because of the high counting rate  environm ent we opted  to  use a very fast U V -em itting scintillator and wave length  shifter which has a fluo­rescent decay constan t of ~2 ns.A fter detailed studies of various scintillator and shifter m ateria l we selected the NE104-BBOT combi­nation  which produces pulses w ith 10 ns FW HM . Our requirem ents for spectral emission were m et by Nuclear Enterprise w ith a rejection factor of 25%. We m ain­ta in  a yield of > 7  photoelectrons/M eV  deposited in all modules. Several m odules were tested  in the TR IU M F meson beam . T he energy resolution for a 50 MeV elec­tron  beam  entering the  centre of the m odule wasa_ _  5.7%E  ~  V E ( GeV) ‘This is com patible w ith a contribution from  sampling fluctuations of 5% and from  photostatistics of 2.5%.D uring the  past year we bu ilt and tested  the two endcap detectors. B oth encaps were installed in the m agnet a t Brookhaven and tested . From  d a ta  taken in the  M ay run we conclude th a t a sam ple of K ^  events leaving ~ 60  MeV in one single m odule is adequate to m onitor the gain and relative balance of the module during data-tak ing . A special trigger is being imple­m ented for the  fu tu re  data-tak ing  runs.Tw o options are being pursued for the  construction of 500 MHz 8-b it transien t recorders: a FADC ap­proach a t BNL based on a new device m anufactured by Tektronix and a po ten tia lly  low cost (<200/channel) device based on the developm ent of a gallium -arsenide charge-coupled device (CCD ) a t T R IU M F. The CCDs being fabricated  on gallium  arsenide by the TR IU M F group are of the buried channel variety. T he diode array consists of Schottky diodes.P ro to type CCD devices have been produced and are undergoing m easurem ents. The devices have 64 charge buckets which would allow storage for 128 ns a t 500 MHz. I t  is intended eventually to  produce a 128- bucket device. The in itia l device has exhibited charge transpo rt over a frequency range of 1 to  500 MHz. A new m icrostructure labora to ry  for production  of the CCDs was bu ilt a t T R IU M F. Developm ent of ancil­lary logic, supervisory and FASTBUS digital readout are also in progress a t T R IU M F in collaboration with M icrotel Pacific Research C orporation.T he beam  counter system  consists of several scin­tillators, two scin tillator hodoscopes, three planes of M W PCs and a Cerenkov counter. All b u t the la tte r were bu ilt a t T R IU M F. T he M W PC s use a fast C F 4 gas m ixture and special hom e-built hybrid  electronics including the post am plifier/d iscrim inator system  built for the central drift cham ber.In the past year the d a ta  acquisition system  was first used for extensive testing  of the  drift cham ber at TR IU M F. It was la ter tested  a t BNL during the May run. The original 2-crate system  was extended to  a 10 FASTBUS crate front-end system . M uch effort has also gone into commissioning and developing testing m ethods for FASTBUS crates full of pipeline TDCs.A t present we are developing a  system  for filter­ing d a ta  prior to  tap ing  using the Ferm ilab Advanced C om puter Program . A nother A C P system  will per­form  off-line analysis a t T R IU M F. T he first step was to install a three-node m ultiprocessor system . Extensive hardw are tests were done to  understand  the function­ing of the system . Software was developed to  allow processing of the d a ta  gathered last M ay as well as analysis of the  drift cham ber test data .W ork has proceeded on reconstruction  routines for the various detector subsystem s. Extensive analysis of the d a ta  collected last M ay is under way. T he gen­eral off-line analysis program  called K O FIA  has been released to  all partic ipa ting  in stitu tions and is being m aintained on six VAXes across the  continent by the T R IU M F group. M uch effort has gone in to  properly docum enting the program .A custom  system  for m anagem ent of all calibration d a ta  needed by the detector has been developed. Con­tro l and m onitoring of all d rift cham ber param eters is now operational via a  CAM AC p a th  separate  from  the d a ta  acquisition pa th . T he VAX-based d a ta  acquisi­14tion program  has been significantly improved.T he E787 m agnet was com pleted in April and the field was m apped by a T R IU M F group. Following the one-week May test run detector assembly has contin­ued through to  the present w ith com pletion scheduled for December. F irst beam  is expected for E787 during the period Jan u ary  to  June 1988.M e a s u re m e n t  o f  K ~  —* Y 7B N L  811 (B N L -B o s to n -C a s e  W e s te rn -N e w  M ex ico - T R IU M F -U B C  c o l la b o ra t io n )(B.L. Roberts, Boston; D.F. Measday, UBCT his experim ent is studying the in teractions of low- energy kaons w ith hydrogen. In January -F eb ruary  d a ta  were ob tained on the reactions K ~ p  —*■ A7  and K ~ p  —► E 7  a t rest. The detector was a superb new N al crystal m anufactured by BICRON. It consists of a central core 26.7 cm in diam eter, 56 cm deep, sur­rounded by a four-piece annulus which takes the di­am eter to  49.5 cm. This detector was tested a t the M IT -B ates Linac and found to  have a resolution of1.8% a t 330 MeV (which is a factor of 3 b e tte r than  TIN A ). T he technological trick  is to  ensure th a t the central core has an extrem ely uniform  response to  a 6 MeV 7 -ray  source (±0.2%  over the front 35 cm).W ith  this crystal it was relatively easy to  separate the captive 7 -rays to  bo th  the A and E°. Previ­ous experim ents had  not clearly observed these 7 -rays bu t had  a ttem p ted  to  ex trac t the A7  peak from  the background w ith debatab le success. T he results are ju s t com patible w ith the calculations of W orkm an and Fearing described in the  Theory section.In a second phase of the experim ent the  LAM PF crystal box has been moved to  Brookhaven and is now installed in the  beam  line. T his device consists of 396 individual crystals (w ith 432 photo tubes) and can determ ine the position and energy of medium -energy photons. T his detector was needed in order to  study the weak radiative decay A —► n j  which is of great in­terest in understanding the weak in teraction properties of the strange quark.In O ctober the  A PC  of Brookhaven approved a fur­ther 1000 h for th is experim ent and a run  is planned for M arch-A pril 1988. T R IU M F has contributed  mainly to  the  detectors, including the p lastic  scintillators. A UBC studen t (A .J. Noble) is s ta tioned  perm anently  at Brookhaven and will be using the A —+ 717 d a ta  as his thesis project.T h e  S L D  e x p e r im e n t(A. Astbury, TRIUMF/Victoria)Im pressive progress have been m ade during 1987 in the commissioning of the  S tanford linear collider(SLC). No fundam ental problem  has been uncovered which would prevent SLC from  ultim ately  achieving the design lum inosity of 6 x 1030 cm -2  s- 1 .In M arch bunches of electrons and positrons m et a t the in teraction  point, and the  m achine was declared completed a t a cost of $115.4 M US. A beam  size of 5 p m  diam eter was m easured a t the  o u tp u t of the  north arc (e_ ) in July. Subsequently the south  arc was tuned, and in Septem ber e+e~ collisions were observed with ~20  p m  d iam eter bunches. T he M ARK II detector was installed in O ctober, and it is anticipated  th a t da ta  collection will commence in April 1988 a t the  rate  of ~ Z Q s/day.T he m agnet steel and coil of the  SLD detector have been erected close to  the in teraction point of SLC. The dewar for the  barrel liquid argon calorim eter (LAC) was delivered to  SLAC in Septem ber and is currently prepared for m odule insta lla tion  to  commence during January  1988.The T R IU M F /U B C /V ic to ria  group had built 60 out of its quo ta  of 75 electrom agnetic m odules for the  bar­rel LAC by the end of the year. The production  in the meson hall extension should be finished during Febru­ary 1988.The modules are tested  by subjecting them  to  high voltage in air, and m easuring the  current drawn. The banded m odule m ust sustain  3000 V and have a to ta l current drain of <1 p A  in dry air. T he p ro to type mod­ule produced in liquid argon a clean signal for cosmic- ray muons, well separated  from  the  electronic noise, w ith the collected charge close to  the predicted value (Fig. 12).EM co sm ic  sp e c tru m  (E2) 4 .0  kVqVt channelFig. 12. Histogram of charge collected from a single channel of the prototype module.15During production  high standards of cleanliness and quality  control have been essential to  ensure uniform ity in the final p roduct. T he instrum enta tion  developed in the group has been invaluable in achieving these goals. Fully au tom ated  system s interfaced to  PC s have been bu ilt for m easuring tile sizes, tower capacities, and m onitoring the current drains of individual towers.T he T R IU M F /U V ic engineers have assum ed full re­sponsibility for the  design of the “cryogenic earthquake snubbers” which pro tect the  SLD LAC in the event of a m odest quake. A p ro to type is under construction and will be tested  early in 1988.T he group has assum ed responsibility for the  design and building of a device capable of m onitoring the pu­rity  of the  liquid argon of the  LAC during the operation  of the SLD detector.T he T R IU M F /U B C /U V ic  group continues to  play a very active role in the  developm ent of software for the experim ent. In particu lar, the  co-ordination of all the calorim etry software and the  M onte Carlo simu­lation of hadron showers are the responsibility of the C anadian group.T he group have taken  responsibility for developing the system  th a t will test the electronics resident on the dewar prior to  installation . T his electronics digitizes the charge on each tower and produces a m ultiplexed signal of 160 towers on a  single optical fibre. This arrangem ent significantly reduces the cost of cables for the 41,000 channels o f the calorim eter.16N U C L E A R  P H Y S IC S  A N D  C H E M ISTR YE x p e r im e n t  266I n i t ia l  s tu d ie s  o f  th e  (n ,p ) r e a c t io n  o n  l ig h t  n u c le i(K.P. Jackson, TRIUMF)T he prim ary  purpose of E xpt. 266 was to  provide precise calculation of the (n,p ) reaction as a probe of B q T , the  d istribu tion  of Gamow-Teller s treng th  for isospin-raising transitions. T he accurately  known f t  values for the /3~ decay of 6He, 12B and 13B to  the ground s ta tes of the  daughter nuclei provide ideal op­portun ities for th is  calibration. Analysis of m easure­m ents of the (n,p) reaction a t 0° on 6Li, 12C and 13C a t E n — 198 MeV has been com pleted and the results accepted for publication  in Physics Letters B.E x p e r im e n ts  268 , 434Iso v e c to r  g ia n t  re so n a n c e s  in  208P b (n ,p )  a n d  120S n (n ,p )  (M. Moinester, TRIUMF/Tel-Aviv;B. Spicer, Melbourne; S. Yen, TRIUMF)D uring M ay d a ta  were taken  for the 208P b (n ,p )  reaction a t 458 MeV and for the  120S n (n ,p ) reac­tion  a t 298 MeV. Together w ith the previous d a ta3>01SuCO£XaX  0b  2 n AX100 20 40Excitation  Energy (MeV)Fig. 13. The 458 MeV 208P b (n ,p )  d a ta  at average scatter­ing angles of 2 .0°, 3.4°, 5.7° and 8.2°. The dashed lines are an estim ated background to the peaks.for E xpts. 268 and  376 [208P b (n ,p )  and 90Z r(n ,p ) at 198 MeV], these d a ta  form  a comprehensive d a ta  set to  study  the energy- and A -dependence of isovector spin giant resonances in heavy nuclei. Figure 13 illus­tra te s  the 458 MeV d a ta  for Pb. T he absence of any prom inent forw ard-peaking s tructu res indicates th a t the  G T  is largely Pauli blocked. T he sharp peak at 5 MeV excitation  in 208T1 is identified as the T> spin dipole on the basis of its angular d istribu tion  and cross section (see Fig. 14) and on the  basis of RPA predic­tions for the  excitation energy [Krm potic et al., Nucl. Phys. A 342, 497 (1980); A uerbach et al., Phys. Rev. C 30, 1032 (1984)]. T he broad  peak centred about 15 MeV is ten tatively  associated w ith the T> spin isovector m onopole predicted to  lie a t 13.5 MeV ex­citation  [Auerbach et a l ,  op. cit; Klein, private com­m unication]. T he presen t large s ta tis tica l uncertainties for the 15 MeV peak do not allow a significant com par­ison of its angular d istribu tion  shape w ith calculations. The off-line analysis of the  298 MeV 120S n (n ,p ) da ta  is still in progress. T he spin dipole is strongly excited. The 120Sn(n, p) d a ta  also exhibit a feature which might be the spin isovector m onopole b u t which is less prom i­nent th an  in 208P b (n ,p )  because the spin dipole is less thoroughly Pauli blocked in  120Sn th an  in 208Pb.198.4 MeV 458.4 MeV SGD R E =  0 -  6 .3 MeV0CM (degrees)Fig. 14. Angular distributions of the 5 MeV peak and back­ground under the peak for the 208P b (n ,p ) d a ta  at both 198 and 458 MeV. The solid curve is a DWIA calculation, based on dipole wave functions containing simple linear superpo­sitions of all possible 1 hio lp - lh  spin dipole configurations.170 30  60  90 120 150 180Deuteron c.m. angleFig. 15. Dependence upon centre-of-mass reaction angle of the change in €is , the sin^ com ponent of polarim eter azim uthal d istribution, normalized to change in Px , the sideways polarization of the beam.E x p e r im e n t  300P o la r iz a tio n  t r a n s f e r  in  th e  pp —* d r  r e a c tio n(D. Hutcheon, TRIUMF)T he m edium  resolution spectrom eter and its focal plane polarim eter (F P P ) were used to  m easure the po­larization  of deuterons from  the reaction pp  —► d r  a t 507 MeV. T he quan tity  of g reatest in terest in resolv­ing am biguities of p a rtia l wave am plitudes is K ss, the transfer o f vector polarization  to  the deuterons from  a sideways-polarized pro ton  beam .We have m easured azim uthal (<j>) distribu tions of scatterings in the  F P P  a t seven pp  —► d r  reaction an­gles. These were Fourier analysed to  ex trac t el3, the coefficient of the sin<f> te rm  (norm alized to  e0 =  1 ) f° r proton beam  polarization  in the + X  and —X direc­tions. T he polarization  dependence ( A e i s) / ( A P X) is p lo tted  in Fig. 15. T his quan tity  is proportional to  the  p roduct o f K ss and the vector analysing power of the  F P P ; there is an additional contribu tion  from  one of the  com ponents of tensor polarization, <21- In the coming year we will m easure the polarim eter analysing powers using the polarized deuteron beam  of SaturneII. T his will allow q uan tita tive  com parison of our d a ta  w ith various p a rtia l wave am plitude fits or calculations.E x p e r im e n t  319R e la tiv is t ic  m e d iu m  e ffec ts  a t  in te rm e d ia te  e n e rg ie s  (D.K. McDaniels, Oregon)An im p o rtan t developm ent has seen the introduction of a relativ istic  trea tm en t of proton-nucleus scatter­ing s ta rtin g  from  a  D irac phenom enological approach.Im petus for th is theoretical approach was provided by the successful description of the  analysing power A y and the spin ro ta tion  function Q for the elastic scat­tering of 500 MeV protons by 40 Ca. T his approach was pu t on a firmer basis through the developm ent of a relativ istic  impulse approxim ation (RIA). These ap­proaches suggest th a t the proton-nucleus optical po­tentials involve large a ttrac tiv e  Lorentz scalar and re­pulsive vector contributions. I t is im portan t to  extend these com parisons to  inelastic sca ttering  processes. In­elastic scattering  to  the  continuum  a t interm ediate en­ergies which is dom inated by quasielastic scattering  provided a useful way to  m ake the com parison with recent RIA calculations.RIA calculations involving strong scalar and vector fields have enjoyed a m easure of success in describing elastic p roton sca ttering  a t 200 MeV and above. To extend the use of these calculations to  inelastic sca tte r­ing Horowitz and Iqbal [Phys. Rev. C 33, 2059 (1986)] have recently calculated spin observables for quasielas­tic p roton scattering  in the RIA. T he RIA approach for quasifree scattering  is based on a covariant form  of the am plitudes describing the N N  in teraction  while the scattering is described th rough the  use of the Dirac equation. In the  nuclear m edium  the strong scalar and vector po ten tia ls enhance the  lower two compo­nents of the 4-com ponent D irac wave functions. In the trea tm en t of Horowitz and Iqbal th is enhancem ent is param etrized by an effective m ass M*  which can be calculated in an eikonal model. Q uasielastic scattering  to  the  continuum  is an a ttrac tiv e  problem  to  study  be­cause it minimizes the nuclear s tru c tu re  dependence of final states. By focusing on the spin observables a t the m axim um  of the quasielastic peak, m ultiple scattering and distortion  effects are fu rther minimized.We have m easured differential cross section and analysing power d a ta  for the  inelastic scattering  of 290 MeV protons by a 208P b  target using the polarized beam  and MRS facility a t T R IU M F. A broad range of excitation  energy (0-160 MeV) has been studied over the 4°-26° angular range. A t the largest angles up to  three different m agnetic field settings for the MRS were needed to  cover an excitation  energy range which included the quasielastic peak. T he incident protons were scattered  from  a 51 m g /cm 2 208Pb target. Beam intensity  (1-5  nA) was m easured w ith a Faraday cup. T he beam  polarization was m onitored by a  polarim eter in the  beam  line.The RIA trea tm en t is expected to  do a good job  of describing various spin m easurem ents a t the quasifree peak since the reaction m echanism  will be a single-step process. Analysing powers m easured in the present ex­perim ent are shown in Fig. 16. T he A y (9) value a t each angle was obtained by averaging the  spectrum  over a18# L(deg)Fig. 16. Analysing powers for the quasifree peak obtained w ith 290 MeV protons scattering from 208 Pb. The two dashed curves correspond to  relativistic impulse approxi­m ation predictions for effective mass values of M* — M  and M* =  0.83 M . The open squares show the free surface response predictions.5 MeV interval of excitation  energy centred a t the  loca­tion of the quasifree peak. The location of the quasifree peak was calculated using relativistic kinem atics plus an energy shift. T he RIA predictions for M* = M  (M  =  nucleon mass) and 0.83 M  are shown on the figure. T he au thors of the  RIA trea tm en t obtained a value of M* =  0.83 M  on theoretical grounds. In the RIA model the  effective m ass M*  is proportional to  the average scalar field stren g th  S ,  v ia M * — M  + S.  These d a ta  support an  effective m ass M*  =  0.77 M  if the  trend  of the calculation continues.E x p e r im e n t  327S tu d y  o f  th e  (7r+ , 7r+ 7r_ ) r e a c t io n  o n  le O , 28Si a n d  40C a  a t  T*- = 2 4 0  a n d  280 M eV(N. Grion, INFN Trieste)T h e  m easu rem en t o f th e  (jr"*", ) reac tio n  on  le Oa t 280 MeV was com pleted during the  Ju ly -A ugust in­tense beam  period. A dditional m easurem ents to  com­plem ent the  d a ta  from  the 1986 runs were taken  in or­der to  m ore com pletely cover the allowed phase space. Results from  the 1986 run have been published [Grion et al., Phys. Rev. L ett. 59, 1080 (1987)].T he T R IU M F QQD spectrom eter was used to  detect the outgoing ir~ in the  energy range of 35-110 MeV at lab angles of 50°, 80° and 115°. The CARUZ was used to  detect the  7r+ in coincidence w ith the QQD and de­tected  pions covering lab angles from  22.5-127.5° on the opposite side of the beam  from  the QQD. The CARUZ is a large solid angle device (0.20 sr) con-Fig. 17. The measured trip le differential cross section shown as a function of the ir~ energy for a CARUZ central angle of 50° and a QQD angle of 80° compared to theoret­ical predictions of Oset and Vicente-Vacas.structed  prim arily  from  a stack of five scintillators. It measures the energy of the  pion by stopping it in the scintillator m ateria l and m easuring the to ta l light out­put. T he pion tim e of flight is also m easured and in com bination w ith the energy inform ation and d E /d x  from  the first scin tillator in the stack  enables the easy m ass-separation of pions from  electrons and protons. The CARUZ m easures pions w ith energies in the range of 8-60 MeV w ith a resolution of b e tte r th an  2 MeV. A paper describing the  characteristics of the CARUZ in more detail has been accepted for publication in Nucl. Instrum . M ethods.Analysis of the 1987 d a ta  has no t yet been fully com­pleted bu t results are consistent w ith those from  the analysed 1986 d a ta . T he theoretical model of Oset and Vicente-Vacas [Nucl. Phys. A 454, 637 (1986)] provides the  m ost com plete description of the experim ental ob­servables available in the  lite ra tu re  and describes many of the observed features in the data . A full-length pa­per in collaboration w ith Oset and Vicente-Vacas de­scribing the full set of experim ental m easurem ents is being w ritten.The m easured fourfold differential cross sections d4T  al dTw+ dCln+ dTw-dClw-  were in tegrated  over the energies and angles of the  7T+ 7r-  pairs extrapolating  to  unm easured p arts  of the phase space. The mea­sured to ta l cross section for the  reaction is found to be 2.95 ±  0 .45 //b in good agreem ent w ith the full the­oretical model m entioned above. Partia lly  integrated cross sections can also be com pared to  the model. Fig­ure 17 shows the trip le  differential cross section in­tegrated  over 7r+ angles in the  CARUZ com pared to  predictions of the model. T he dashed curve represents the prediction when the  renorm alization of the ou t­going real pions (or equivalently, the binding of theseC o in c id e n c e  (7t+,7t )_. i  i i ie =+ 80 ’± 3'e w+=- 50 ±28’2 0 0 -T (MeV)7T —19oaMteNx>+kHTJikH-O+kcT3lkcb•oFig. 18. The measured energy distribution of the x + in the CARUZ for the CARUZ a t 50° and the QQD at 50° accepting in the energy range of 60-110 MeV compared to  the model predictions.the  binding of these pions in the  nuclear m edium ) has no t been included while the  full line includes the bind­ing effect. T he inclusion of the  binding constitutes the full model which describes the to ta l cross section. Note th a t all quantities are given in the laboratory  frame.T he energy spectrum  of detected 7r+ particles for one subset o f the  d a ta  is shown in Fig. 18. The curves have the sam e m eaning as in Fig. 17. The full cal­culation fails to  reproduce to  m easured energy d istri­bu tion  which is peaked a t much lower energies than  the  model results T he failure is not serious and likely sim ply points to  the  lack of including a full trea tm en t of the inelastic reactions th a t the exiting pions can un­dergo. T he m odel includes absorption in the final sta te  b u t no t inelastic scattering.E x p e r im e n t  329T h e  E E L L  e ffec t in  4 H e(Y.M. Shin, Saskatchewan)Inspired by the success of the  EELL (Ericson- Ericson-Lorentz-Lorenz) effect in describing inelastic pion scattering  for 0+ s ta tes in 12C [e.g. Lee et a i ,  Phys. L ett. 174B , 147 (1986)], we have undertaken a sim ilar investigation of the 20.1 MeV 0+ s ta te  in 4IIe. Differential cross sections for 50 MeV pions incident upon a  1.7 cm thick liquid 4He ta rg e t were m easured using the T R IU M F QQD spectrom eter a t lab angles of 30°, 45°, 60°, 117.5° and 120°. No peaks correspondingto  the 20.1 MeV s ta te  were observed, thus placing an upper lim it of 3 pb /sv  for each of the above angles. The upper lim its were due to  backgrounds from  m ultiply scattered  elastic and deep inelastic pions from  target walls and fram es th a t  rem ained even after tigh t cuts on target position and thickness, tim e of flight of pions to ta rget, tim e of flight of pions through the QQD, various optical functions [0o- f ( 6 f ), Xq90, y ^ o ]  andm om entum  differences from  W C4 and  W C5. Em pty target runs showed th a t  the  rem aining backgrounds rem ained flat in the vicinity where the 20.1 MeV sta te  should be. Only theoretical calculations w ith appre­ciable EELL param eters, such as elastic scattering pa­ram eter, transition  am plitude param eter of (1.5,1.5) or (2 .0,2 .0), are consistent w ith the above experim ent lim its, as shown in Fig. 19.E x p e r im e n t  331S p in  t r a n s f e r  m e a s u re m e n ts  in  it + d —> p + p(G. Jones, UBC)An intensive program  of spin-dependent m easure­m ents of the  p  + p  —*■ d + x  reaction has been directed in recent years to  the  experim ental determ ination  of a unique set of am plitudes for th is  reaction. M ost of this work has involved the m easurem ent of spin-correlation param eters ob tained by bom barding a polarized pro­ton target w ith a polarized p ro ton  beam . It has been clear, however, th a t additional m easurem ents depend­ing on the deuteron spin are required before a unique am plitude determ ination  can be obtained. T he first of these were i tn  analysing power m easurem ents, carried ou t (for the inverse reaction) by utilizing a polarized deuteron target. T he m ost com prehensive set was pro­vided by the K arlsruhe group a t SIN. T he o ther m ea­surem ents required are the spin transfer param eters.Cw<6Fig. 19. Theoretical calculations for 28.1 MeV sta te  in 4He using charge density and charge transition  density.Coincidence (7t+,7t“)-  + 50 ’± 3*e_ . «  —5 0 ’±28 'T (MeV)20KINEMATIC CORRELATIONS Corbon angle (unfiltered)2 0 0   t - -i--------- rANGULAR CORRELATION COPLANARITYFig. 20. Polar and azimuthal (coplanarity) angular corre­lations for the rrd —► 2p reaction using 205 MeV pions.A lthough these have been known to  be extrem ely im­p o rtan t in constraining the allowable partial-w ave am ­plitude fits, they have experim entally  been the m ost challenging to  perform .O ur approach to  m easuring the spin transfer param ­eters has also utilized the inverse reaction, nam ely the determ ination  of the  polarization  of one of the ou t­going protons when the pion is absorbed on a polar­ized deuteron ta rge t. To th is end, a p roton polarim e­ter has been constructed , a polarim eter sim ilar in de­sign to  those developed a t SIN and LA M PF, involving use of a carbon analyser w ith m ulti-w ire drift cham­bers before and after the carbon to  provide the nec­essary tra jec to ry  inform ation. T he production of pro­ton pairs from  background reactions associated w ith pion absorption  in the nuclear ta rg e t m ateria l was distinguished from  the  reaction of in terest by impos­ing appropria te  kinem atic constrain ts on the two pro­ton events. Figure 20 shows the po lar and azim uthal (coplanarity) angular correlations resulting when the deu terated  target was employed, while the lower curves in each case indicate the corresponding quality ob­tained using a norm al hydrogenated target instead. It is clear th a t the jo in t im position of cuts on these two d istribu tions reduces the background contam ination to  the level of a few per cent. In order to  reduce the am ount of d a ta  stored on m agnetic tape, a front-end processor (SEN J - l l  S ta rb u rst) was employed to  re­jec t any events associated w ith a scattering  angle in the  carbon of the  polarim eter by less th an  6°. Fig­ure 21 dem onstrates the  effectiveness of this system  for elim inating the large num ber of “stra igh t-th rough” events which would otherwise have sa tu ra ted  the d a ta  acquisition system . B oth Figs. 20 and 21 were ob­tained for incident pions of 205 MeV kinetic energy. The d a ta  analysis algorithm s have been tested  on a set of unpolarized ta rg e t runs. One im portan t checkO 'co120 4 0  -4 0  -120  --200-20 -12 -4 4 12X angle20Carbon angle (filtered) 200  c---------rFig. 21. Two-dimensional plots of proton scattering an­gle in the 7 cm thick carbon analyser of the polarimeter. The “unfiltered” events are a sample of those events satisfy­ing cuts based only on reaction kinematics. The “filtered” events are the result when a > 6 ° scattering angle is imposed by the J ll-S ta rb u rs t.°6.0 8.8 11.6 14.4 17.2 20.0T H E T AFig. 22. Proton polarization resulting when an unpolarized deuteron target is employed. The polarization is plotted against the scattering angle in the carbon analyser. The solid lines are the angle-independent least squares fits to the data.21for system atic  errors is the requirem ent th a t the  cal­culated polarization is independent of the  scattering  angle of the proton in the carbon of the  polarim eter. Figure 22 shows such a result for the unpolarized ta r­get. For th is reaction a nonzero “norm al” polarization is expected (equal to  the analysing power of the inverse pion p roduction  reaction). However, no “sideways” po­larization  can result from  such a reaction. Some side­ways polarization  will, however, develop as the proton precesses while travelling through the m agnetic field surrounding the polarized target. Development of the d a ta  analysis algorithm s to  account for th is precession is currently  under way. M easurem ents relating to  the spin transfer param eters Ki„ and K , s were m ade w ith the  target polarized (vector polarized to  greater than  30%) a t pion energies of 105 (K t , only), 140, 180, 205 and 255 MeV. Because of constrain ts imposed on the emerging protons by the  m echanical struc tu re  of the polarized ta rge t, the  K t a m easurem ents (which em­ployed a longitudinally polarized ta rge t) were taken w ith the polarim eter s itua ted  a t an angle correspond­ing to  30° (c.m .s.), whereas the corresponding angle for the  K , s m easurem ents (using the target in a sideways orientation) was 90°.E x p e r im e n t  337E n e rg y  d e p e n d e n c e  o f  T20 a n d  7-21 in  vd  e la s tic  s c a t t e r in g  (G.R. Smith, TRIUMF)D ata  acquisition and analysis for E xpt. 337 has been com pleted during the course of the  year. A draft of the final publication  has been prepared and is being circu­lated  to  the  collaboration. T his final publication ad­dresses the  energy dependence of the tensor analysing powers T20 and 7-21 for 7rd  elastic scattering. M ea­surem ents of T20 were ob tained  for pion bom barding energies of 180, 220 and 256 MeV. M easurem ents of 7*21 were obtained for pion bom barding energies of 134 and 220 MeV. Six-point angular d istribu tions were ob­ta ined  for the T20 m easurem ents, and twelve-point an­gular d istribu tions were acquired for the m easurem ents of 7*21- T he results are com pared w ith th ree-body cal­culations where effects relating  to  pion absorption are seen to  play an im portan t role.O ur previous work in th is  area includes m easure­m ents of T20 a t 134 and 151 MeV [Phys. Rev. Lett. 57, 803 (1986)], m easurem ents of 7*21 a t 180 MeV [Phys. Rev. C 35, 2343 (1987)], and m easurem ents of pzz [Nucl. Instrum . M ethods A 254, 263 (1987)]. To­gether w ith the current results, these d a ta  provide a system atic basis for com parison to  theoretical predic­tions over the  (3,3) resonance region.M easurem ent of a  given spin observable Tkq is ac­com plished by choosing an appropriate  orien tation  ofthe deuteron spin alignm ent axis, such th a t the contri­bu tion  of o ther spin observables is elim inated or m in­imized. M easurem ents of T20 are perform ed in an ex­perim ental configuration w ith longitudinal ta rget mag­netic field. This orientation results in a clean, simple expression for T20 which involves only the polarized and unpolarized nd  elastic cross sections <x(pol) and cr(unp), and the target tensor polarization pzz accord­ing to:rr _  \/2 (  o-(pol)Pzz (1)In order to  em phasize the spin observable T21, the appropria te  ta rget m agnetic field orientation  is 45° to  the  incident beam  axis, in the  horizontal plane. The m easured spin observable 7*21 may then be expressedasr 2l =g(pol) V ^ P z z  W unP)-  1(2)(3)In a T21 experim ent the quan tity  actually  measured is a m ix ture of T2i, T20 and T22 according to  Eq. (2) which we refer to  as 7*21. T he dom inant contribution to  7*21 comes from  X21, since the T20 term  is weighted by 1/(2  • \ / 6) and the T'2'2 term , weighted by a fac­to r of 1 / 2 , is predicted to  be sm all in the backward hem isphere where th is experim ent was perform ed. We have chosen to  present our results as the specific linear com bination of tensor observables given by Eq. (2) be­cause th is linear com bination can be expressed entirely in term s of experim entally  m easured quantities.T he m ain characteristics of the  detection system  are as follows: A solid angle of 27 m sr for each of six inde­pendent arm s was defined by a pion scin tillator (7r2, ) located 1 m  from  the polarized ta rge t, of dimensions 9.Ox 30.0 cm 2. Together w ith another scintillator (ttI,-) a t 0.5 m  radius w ith dim ensions 4.9 x 16.5 cm2, this constitu ted  one of six pion telescopes. Each of the pion scintillators was 3.1 m m  thick, and  was tilted  and raised or lowered vertically to  correspond to  the actual pion tra jectories deflected th rough  the m agnetic field of the polarized target.Each pion telescope was placed in  coincidence w ith an associated recoil deu teron  arm  consisting of 3 scin­tillators. The first scin tillator (D lj)  a t a radius of 1.3 m  from  the ta rg e t was a th in  (3.2 m m ) scintillator of dimensions 9.0 x 40.0 cm 2 which provided T O F  as well as energy loss (A E)  inform ation. Following this scintillator was an alum inum  absorber, whose thick­ness was adjusted  so th a t  deuterons stopped in the fol­lowing 1.27 cm thick  scin tillator (D2,) of dimensions227003 0 0  - f   ..........................................................................................     , , i |4 0 0  6 4 0  8 8 0  1120 1360 1600D e u t e r o n  E n e r g y  (E + AE)Fig. 23. A typical two-dimensional spectrum  of the deuteron TO F (vertical axis) vs the sum of the deuteron pulse heights in the A E  counter (D l) and the E  counter (D2) is shown. The deuteron band is in the upper right. The other events are protons from quasielastic scattering, absorption and deuteron break-up reactions. The c.m. an­gle corresponding to  this histogram  was 140°.9.0 x 41.0 cm 2. The th ird  was a veto scintillator (D3j) of dim ensions 9.0 x 41.0 cm 2, 6.4 m m  thick.T he flux of the incident beam  was counted directly w ith scintillators SI and S2 in coincidence, each of which was 1.6 m m  thick. T he size of S2 was chosen such th a t its image a t the target would be sm aller than  the ta rg e t itself. P ro tons in the  incident beam  were reduced by using a differential degrader (2 m m ) near the m idplane of the  M i l  channel. Those rem aining in the  beam  were elim inated by [placing pulse height requirem ents on SI and S2 in the  trigger, defined by SI • S2 ■ S I • S2 • 7r l j  • 7r2j • Dl* • D3j. T he incident flux was typically 2 x 1067t+ /s . Explicit m easurem ents of the background arising from  quasielastic nd  sca tter­ing from  the contam inant carbon and oxygen nuclei in the polarized target m ateria l were also m ade by replac­ing the deu tera ted  butanol ta rg e t w ith an equivalent am ount of nondeu terated  bu tanol (C 4H9OH).T he final analysis o f the d a ta  was perform ed by con­structing  polygons around the 7rd elastic events iden­tified in two-dim ensional histogram s of the deuteron T O F  vs the deuteron to ta l energy E  +  A E ,  where A E  corresponded to  the  pulse height in D l, and E  to  the  pulse height in D2. T he resulting sca tterp lo t provides good particle identification which clearly sep­arates deuterons from  protons. A typical (foreground) sca tterp lo t o f these quantities is shown in Fig. 23.The tensor polarized target consisted of 2.4 cc of frozen 1 m m  diam eter beads contained in a th in  walled teflon basket m easuring 22 x 18 x 6 m m 3. The teflon basket, which also served as support foran NM R pickup coil, was im m ersed in a m ixture of 3H e /4He in the m ixing cham ber of a d ilu tion  refriger­ator. The beads were com posed of a m ix ture of 95% fully deu terated  N -butyl alchohol (C 4D 9OD) and 5% D 20  in to  which deu tera ted  EH B A -C R V was dissolved to  a m olecular density of 6 x 1019 a tom s/m l. T he polar­izing field of 2.5 T  was provided by a superconducting split pair solenoid w ith a horizontal m agnetic field axis either 0° (for the T20 m easurem ents) or 45° (for the 721 m easurem ents) to  the incident beam  axis. T his align­m ent was carefully checked to  w ithin 0.2° by means of a series of m agnetic field m easurem ents a t various points in space dow nstream  of the polarized target.T he T21 d a ta  were acquired w ith the target in frozen spin mode a t a  holding field of 1.25 T . T he T20 da ta  were acquired w ith the ta rg e t m agnetic field a t 2.5 T. T he target tensor polarizations achieved in th is exper­im ent varied from  run  to  run, from  0.094 ±  0.010 to  0.173 ± 0 .0 1 0 .Three-body calculations employing Faddeev equa­tions have been perform ed by a num ber of theory groups around the globe. T he results of this exper­iment are com pared to  a subset of these calculations in Fig. 24. T he d a ta  include m ost of the results of this experim ent. The calculations are from  Blankleider and Afnan [Phys. Rev. C 2 4 , 1572 (1981)]. The solid curve corresponds to  the ir full calculation. The dashed curve corresponds to  the ir predictions w ithout pion ab­sorption and rescattering , which was accomplished by om itting the P \\-kN  two-body input. Clearly, the da ta  are b e tte r described by the la tte r  calculation than  by the former.T he P n  inpu t to  the  three-body calculations has been a  source of difficulty for some tim e now. This te rm  is sp lit in to  pole and non-pole contributions which account for true  pion absorption and rescattering, re­spectively. T he crux of the theoretical difficulty is th a t for some p a rtia l waves the pole te rm  contribution  will be Pauli blocked in the two-nucleon in term ediate state, fn such cases the non-pole term  acts alone and, with no pole term  contribu tion  to  cancel it, has a  consid­erable im pact on the  results o f the calculations. The Pauli blocking of the  P n  pole te rm  is the m ajor source of problem s in the  theory a t the  present tim e.E x p e r im e n t  344E x c i ta t io n  o f  “ s t r e t c h e d ” p a r t ic le -h o le  s ta te s  in  c h a rg e  e x c h a n g e  r e a c tio n s  (J.W. Watson, Kent State)We m easured cross-section angular distributions for “stretched” particle-hole sta tes excited in (n ,p ) reac­tions a t 300 MeV, w ith the CH A RG EX  facility for the230 «.m. ( d e g )Fig. 24. A t each of four representative pion bom bard­ing energies for ird elastic scattering, values of the tensor analysing powers T20 and r2i are shown. The solid curves depict the full three-body predictions of Blankleider and Afnan, and the dashed lines correspond to  the same calcu­lations w ithout the P\\  am plitude.MRS spectrom eter. In a stretched sta te  the p a rti­cle and the hole are both  in “stretched” orb its (j p = l p + l / 2 \ j h  — U  +  1 / 2) and their angular m om enta are coupled to  the m axim um  possible J  — jp -f  jh ■ Such sta tes are unique w ith 2hu> of excitation so th a t there is little  mixing w ith o ther possible one-particle- one-hole configurations. For charge exchange nucleon scattering  [(p, n), (n ,p)] a t m edium  energies stretched sta tes are excited alm ost exclusively by the isovector- tensor p a rt of the  nucleon-nucleon in teraction . Thus stretched sta tes have a very simple particle-hole struc­tu re  and are excited in (p, n) or (n ,p )  reactions princi­pally by a single p a rt of the nucleon-nucleon force; for these reasons the ir excitations in (p, n) and (n ,p )  reac­tions provides an opportun ity  to  explore the  nucleon- nucleus in teraction  in a s itua tion  relatively free from com plications.The specific transitions th a t  we studied  were 12C (n ,p )12B (4",4 .5  M eV)[^d5/ 2,7rp3/12] 28S i(n ,p )28A l(6~ ,5.17 M eV )[i//7/2, i r d j / j  120S n (n ,p )12OIn(10“ , ~ 0 .0  M eV)[i//iu / 2, 7rg~f\]T he 10“ streng th  populated  in the  S n (n ,p ) reac­tion appears to  be concentrated  in a single sta te , pre­sum ably because the neutron excess places b o th  the neutron-particle and proton-hole orb its near the nu­clear Fermi surface.E x p e r im e n t  352Z ero  d e g re e  r a d ia t iv e  c a p tu r e  o f  n e u t ro n s(G .W .R . Edwards, Alberta)In Decem ber 1986 E xpt. 352 ( “ZERCO N ” ) moved to  the MRS CHARGEX facility for its  zero degree cross- section m easurem ent of the p ( n ,y ) d  reaction. An LH2 ta rget cell, ad justable between 4 and 6 cm, was con­structed  which allowed the  placem ent of th in  (0.01 in.) plastic scintillators directly  on the walls surrounding the cold gas and the viewing of these scintillators (one upstream  and one dow nstream  of the ta rge t) through two periscope-like air guides. T h is arrangem ent was designed in order to  provide a clean signal th a t an event producing a deuteron had  occurred in the target cell, and to  remove the  substan tia l background from  (n ,d )  reactions on carbon which had proven a problem  when ZERCON was running on the 4A line. T he other m a­jo r problem  associated w ith  the  earlier ZERCON runs, the lack of a  resolution capable of clearly separating the p ( n ,7 )d reaction from  the m uch more probable p(n,7r°)d reaction, was expected to  be solved by the sm all energy spread (<1  MeV) of the  neutron beam  produced in the CH A RG EX  facility (from 7Li(p, n )7Be on a 220 m g /cm 2 Li ta rge t) and by the use of the MRS, a spectrom eter w ith good resolution and well-known properties.In Decem ber 1986 runs a t energies 240 MeV and 300 MeV were attem pted . T he th in  scintillators which were supposed to  reduce the background under the (71, 7 ) peak perform ed poorly during th is run , and as a result the  usefulness of the 300 MeV d a ta  is some­w hat dubious. T he 240 MeV ( n ,7 ) peak while sitting  on a large background, provides a point of overlap with the Mainz d a ta  set, w ith  s ta tis tica l errors in the neigh­bourhood of 6-7%  (after background subtraction).In A ugust ZERCON resum ed running a t energies of 360 MeV, 410 MeV (in terrup ted  by the A ugust prob­lems w ith the T R IU M F rf  transform er and completed240 50  100 150 200MomentumFig. 25. The num ber of deuterons from the reactions np —► dy and np —* dw° at 410 MeV are shown as a function of focal plane position for a full target (upper panel). Below is shown the yield from an em pty-target run, normalized to  the same beam  flux.in O ctober) and 460 MeV. In the in terim  the light- gathering efficiency of the  LH2 interior scintillators had been considerably increased by an im proved periscope geom etry and by the sanding of the back of these scin­tillators. T he runs a t these energies were quite success­ful. T he na tu ra lly  lower background a t the higher ener­gies, combined w ith the stringent condition imposed by the interior scintillators, reduced the background sub­traction  problem  to  an easily m anageable size, and the resolution of the  spectrom eter kept the (n, 7 ) peak well separated  from  the (d, ir°) peak. Enough counts were accum ulated a t each energy to  provide 5% statistics after the double norm alization of p(n,  7 )d to  p(n , 7 r ° ) d  and p ( n ,7r°d to  p (n ,p )n  (required because the accep­tance of the MRS was not sufficient to  include both  the (n, 7 ) and elastic scattering  peaks a t the  energies above the pion production  threshold). Figure 25 shows the results of the  prelim inary analysis of the 410 MeV data .E x p e r im e n ts  3 5 5 /4 5 9E x c h a n g e  e ffec ts  in  0+ —► 0-  in e la s tic  s c a t te r in g  (J. King and D. Frekers, Toronto)T he 0+ —► 0“ transitions are of special im portance in the study  of the in teraction  of interm ediate-energy pro­tons w ith nuclei. In nonrelativ istic  im pulse approxim a­tion calculations one finds the analysing power A y — 0 under tim e reversal invariance if only the direct te rm  is included. However, the  exchange term  does not vanishunder tim e reversal, and therefore a  finite A y measures the exchange p a rt o f the  in teraction.Also, in a  longitudinal-transverse representation  for the in teraction  t  m atrix , we find the transverse term s vanish for the  0+ —► 0~ transition , which m eans th a t the  spin-orbit p a rt of the  in teraction  does not con­tribu te . A nd since the central te rm  is expected to  be weak, the cross section should be determ ined m ainly by the m agnitude of the tensor p a rt of the interaction.We have m easured d a /d f l  and A y a t E p =  200 MeV for the T = 0  0+ —► 0“ transition  in 160  using both solid oxide targets  and a “waterfall ta rg e t” . For the description of our d a ta  a  microscopic optical potential, which gives good fit to  the  elastic scattering  d a ta , has been used in DW IA calculations w ith bo th  the Ham­burg density-dependent (DD) poten tia l and  the 1985 Love-Franey (LF) effective in teraction . T he results are shown in Figs. 26 and 27. A lthough the tensor compo­nent of the interaction  dom inates in bo th  cases, neither calculation gives a satisfactory  description of the  data.A relativ istic  trea tm en t is quite different to  nonrela­tivistic calculations in the  sense the nonvanishing val­ues for the analysing power of the 0+ —» 0“ transition  cannot be related anym ore to  only the exchange parts of the in teraction . We have perform ed a relativistic calculation (D REX ) using the im pulse approxim ation w ith expicit exchange included. As can be seen from Fig. 28 the results underestim ate  the  cross section by roughly a factor of 2.5, although the shape of the cross section as well as of the analysing power is significantly b e tte r described.Refinements of the DD and D REX  calculations are in progress and a m easurem ent a t Ep =  400 MeV is presently under analysis. A much b e tte r  understand­ing of the tensor com ponent of the nucleon-nucleon in teraction is in sight.E x p e r im e n t  365 A  s e a rc h  fo r  th e  t e t r a n e u t r o n(T. Gorringe, UBC and Queen Mary College)We have used the pion double charge exchange (DCX) reaction 4H e(7r_ , 7r+ )4n to  search for the pro­duction of te tran eu tro n s (nuclei containing four neu­trons and no protons). We searched for An bound by 0 to  3 MeV (the upper bound being set by the ab­sence of the decay sHe—>4H e+ 4n), using the TRIU M F tim e projection  cham ber and a high pressure helium gas target. T he experim ent was perform ed on the M9 channel a t tt~ incident energy of 80 MeV, over an an­gular range from  50° to  130°. The acceptance and m om entum  resolution for 50 MeV 7r+ were determ ined studying the elastic sca ttering  Tr^He [see Fig. 29(a)], Careful investigation of the ra te  dependence of these2510° 10°" 0  8 16 24  32  400c.m. (deg)8 16 24 32 400c. m. (deg)Fig. 27. Same as Fig. 26, but for DD interaction.Fig. 26. Cross section and analysing power for the 0+ —♦ 0~ ,T = 0  transition  in leO with the 1985 LF interaction. The dashed (dotted) curve is the tensor (central) contri­bution and the solid curve is the sum of centra and tensor contribution.Fig. 28. Cross section and analysing power from a relativistic calculation. For the dashed curve the results have simply been scaled by 2 .5 .0c.m. (deg)2640 60 80 100 120 140 160 180 7T momentum (M eV/c).40  60 80 100 120 140 160 180 7T+ momentum (M eV/c).Fig. 29. (a) Measured 7r+ m om entum  spectrum  from4H e (r_ , 7r+ ) at 170 M eV /c (80 MeV) and 6 =  50°-130°, after all cuts and flask background subtraction. Arrows in­dicate the region corresponding to  bound te traneutron  pro­duction w ith the experim ental resolution, (b) Measured 7r+ momentum spectrum  from 4He(7r+ , 7r_ )4He elastic scatter­ing at 128 M eV/c (50 MeV). The mom entum  resolution is 11 M eV/c (<r).quantities allowed a correction for the different rates in the T P C  between the two reactions.Figure 29(b) shows the final DCX 7r+ m om entum  spectrum  after all cuts and em pty  target subtraction. I t represents a to ta l of N %-  — 6.01 x 1010 incident neg­ative pions (after deadtim e correction). T he spectrum  contains no peak in the  region of 128 M eV /c signaling te tran eu tro n  production. T he 8 ± 5  counts in the region 128 ±  11 M eV /c are alm ost certainly a ttrib u tab le  to  misidentified positrons. T his is expected, due to  the large positron background and our lim ited e+ rejec­tion efficiency. T he counts a t lower m om enta are from  both  continuum  DCX n + ’s and misidentified positrons. Taking N 4n =  13 as the  lcr lim it of 8 ±  5 (7r ~ ,7r+ ) events in the m om entum  window 128±11 M eV /c cor­responding to  te tran eu tro n  production, the  following cross-section lim it is then  obtained:dad£lN a  .i c pt t g tefi ) <  14—  , / srwhere /  =  0.68 is the fraction  of events w ithin ± a  of the peak centroid, [(NA ) / (A )p t \ tgt is the  target thick­ness in nuclei/cm 2, N v -  is the deadtim e corrected num ber of incident ’s, and eCl the  detector accep­tance.In conclusion we have searched for a peak in the 7r+ m om entum  spectrum  from  n~  DCX on 4He cor­responding to  the production  of bound te traneutrons. We observed no evidence for the ir production and were able to  set an upper lim it on the  production  cross sec­tion of 14 n b /sr. As w ith previous experim ents, the results cannot be considered as excluding the te tra ­neutrons existence.E x p e r im e n t  375F e w -b o d y  p h y s ic s  v ia  th e  xd  b r e a k -u p  re a c tio n(E.L. Mathie, Regina)Analysis of the differential cross-section d a ta  mea­sured la te  in 1986 has proceeded in Regina through­out the  year. A m aste r’s thesis (V. Pafilis) has been com pleted and a publication  describing the results is in preparation . M easurem ents were ob tained for pion bom barding energies of 134, 180 and 228 MeV. M ulti­ple coincidences between six pion arm s and six proton arm s enabled m easurem ent of 36 sim ultaneous time- of-flight d istributions a t each energy. T he results are com pared w ith three-body calculations of Garcilazo, which have recently been revised to  correct an error which led to  a too sm all cross section. In those regions of phase space where the new results and the SIN da ta  have the sam e kinem atics, there exist some differences, which are being investigated before a comprehensive com parison w ith theory is com pleted. It is felt th a t the different approaches used to  correct the d a ta  for the finite m om entum  and angular binning may be the source of the  differences between the experim ents. The target used for the  cross section studies was liquid deu­terium , and explicit m easurem ents of the em pty target flask were m ade to  ensure a sound background subtrac­tion  even in kinem atical regions well away from  the quasifree scattering  peak. M easurem ents of the vec­tor analysing power for the sam e broad range of phase space as for the  cross sections began in December, us­ing the T R IU M F polarized deu teron  target. T he da ta  set includes all three of the  above incident pion ener­gies, w ith m easurem ents of the  relative cross sections for the  ta rg e t in an unpolarized s ta te  (to  enable sensi­tiv ity  to  the  tensor analysing powers) as well as both polarized states, and a background ta rg e t (m ounted in the cryostat a t the sam e tim e as the polarized target cell). The detection system  used in the present experi­m ent for the  7rd break-up reaction is sim ilar to  systems used for m easurem ents of T20 and X21 in the  elastic27scattering  reaction, and is described elsewhere in this annual repo rt (E xpt. 337). M odifications to  th a t sys­tem  involve changes to  the electronic logic configura­tion  so th a t  any of the six pion arm s in coincidence w ith any of the  six proton arm s may trigger an event. The p ro ton  m om entum  is inferred from  the pro ton  tim e of flight. Background reactions are elim inated by pulse height analysis in bo th  the p ro ton  and the pion tele­scopes, and from  the two-dim ensional plots of pion tim e of flight versus proton tim e of flight (where the break-up reaction follows a well-defined locus). Resid­ual backgrounds are sub trac ted  using the background m easurem ents. T he objective of th is experim ent is to investigate the kinem atical regions of th is very im por­ta n t reaction channel of the pion-two-nucleon system  well away from  the quasifree scattering  peak, w ith high sta tistics and careful background m easurem ents.E x p e r im e n t  376G am o w -T e lle r  s t r e n g th  a n d  g ia n t  re so n a n c e s  in  90Zr(rc,p) a t  198 M e V(S. Yen, TRIUMF; M.A. Moinester, TRIUMF/Tel-Aviv;B. Spicer, Melbourne)T he 90Z r(n ,p )90Y reaction has been studied a t a bom barding energy of 198 MeV in a search for com­pact G T + streng th  and to  study  isovector spin giant resonances. No com pact G T + s trength  a t low exci­ta tions was found. Up to  10 MeV excitation in 90Y we ob ta in  a firm  upper lim it of Sp+ =  3.4, and a tigh ter bu t m odel-dependent upper lim it of Sp+ — 2.0. By com parison w ith the RPA calculations of Klein et al. [Phys. Rev. C 31, 710 (1985)] and of Sm ith et al. [Phys. Rev. C 36, 2704 (1987) and private com­m unication], and by exam ination of the  angular dis­tribu tions, we ten ta tive ly  identify the peaks a t 5 and 10 MeV excitation  above the ground s ta te  of 90Y  as being spin dipole (see Fig. 30). I t is surprising th a t the RPA calculations, which were successful in repro­ducing the 90Zr(p, n) d a ta , predict features th a t are much too sharp  and underpredict the  to ta l cross sec­tion  a t forward angles and high excitations. This dis­agreem ent indicates th a t there are likely processes oc­curring which were not adequately  accounted for by the RPA-DW IA calculations, and hence caution m ust be exercised in using such calculations to  reach con­clusions about the significance of the A -isobar in the “quenching” of G T  strength .E x p e r im e n t  377E n e rg y  d e p e n d e n c e  o f  th e  c h a rg e  a s y m m e try  p a r a m e te r  A(Tn,d) in  ird e la s t ic  s c a t te r in g(G.R. Smith, TRIUMF)D ata  acquisition and analysis for E xpt. 377 has been com pleted during the course of the year. A publi­cation describing the results has been subm itted  to Physical Review C. M easurem ents of A (T n , 9) were ob­tained for pion bom barding energies of 143, 180, 220 and 256 MeV. Tw elve-point angular d istribu tions were obtained a t each energy. T he results are compared w ith three-body calculations of A (T n , 9) in which the masses and w idths of the  A  isobars are varied.T he charge asym m etry param eter A(Tff, 6) is definedExcitation Energy (MeV)Fig. 30. Cross sections for the 90Z r(n ,p ) reaction at 198 MeV for 1.8° and 6.4°. The top and bottom  dashed curves represent, respectively, the 0° and 5° calculations of Klein et al. The tall and short dotted  curves represent the 0° calculations of models A and B of Bloom et al. [Can. J. Phys. 65, 684 (1987)], respectively, plo tted  w ith a reso­lution of 2.1 MeV FWHM; the peaks would be taller by a factor 1.4 if p lotted w ith the experim ental resolution of 1.5 MeV FWHM. The dot-dash curves represent the 6.4° cal­culations of Smith et al.; the larger curve is the to ta l cross section, whereas the smaller curve is the two-step contribu­tion only.28in term s of the  differential cross sections <r± for x ± d elastic scattering  a t a  given pion bom barding energy Tw (in MeV) and c.m. scattering  angle 9 according to7+(0)A (T r ,0) =cr-(0) +  a+ (9) (1)T he results of the  experim ent were param etrized in term s of m ass and w idth differences am ong the charge com ponents of the  A  isobar, using the well-known m easures for CSBct = (r_ - r ++) + -(r0 r+ ). (2)T he detection system  used in the present experim ent for m easurem ents of A (T tt,9) in the nd  elastic scat­tering reaction is sim ilar to  system s used for m easure­m ents of T20 and T21 in th is reaction , and is described elsewhere in th is  progress report (E xpt. 337). T he ta r­gets used for the studies were solid plastic slabs of C D 2, w ith  an isotopic deuterium  purity  >99% . Two targets were available, w ith areal densities of 224 m g /cm 2 and 405 m g /cm 2. Explicit m easurem ents of the sm all back­ground from  quasifree nd  elastic scattering  on carbon were m ade using graphite  slab targets.The relative differential cross sections were calcu­lated  from  m easurem ents of the nd  elastic scattering  yield, the num ber of incident beam  particles (counted d irectly), the  com puter efficiency (typically 99%), the correction for m ultiple particles in the beam  burst, and the pion fraction  of the  incident beam  f n . T he s ta ­tistical uncerta in ty  associated w ith the relative cross sections was < 1% for each sequence.T he pion fraction of the incident beam  /*  (see Ta­ble II) is the  largest correction to  the d a ta  which is sensitive to  the  incident beam  polarity. Considerable a tten tion  was given to  an accurate determ ination  of this correction. D uring each run, the  e± contam ina­tion of the incident beam  was acquired sim ultaneously w ith the 7r± d d a ta , by digitizing a tim ing signal from a capacitive probe in the T R IU M F proton beam  line w ith respect to  a scin tillator in the  M i l  beam. A separate m easurem ent of the incident beam  fraction was m ade after the experim ent, by lim iting the phase space of the  incident beam  using slits in the TR IU M F cyclotron, such th a t  the  w idth of the incident beam  buckets was ~  0.6 ns, instead of the  usual 2.5 ns. This m ade it possible to  separate  7r± , /r± , and a t each of the  bom barding energies studied  in th is experim ent. A typical spectrum  (obtained using the narrow  beam  bucket) showing the separation  of ^ ± , /i± , and e± at T ,r=180 MeV is presented in Fig. 31. Table II sum m a­rizes the  results of the beam  fraction studies w ith the narrow  beam  bucket m easurem ents.A T  ( n s e c )Fig. 31. The T O F  spectrum  of particles down the M il channel is shown for positive (1) and negative (b) polarities at T,r=180 MeV. From left to  right the peaks correspond to  pions, muons and electrons or positrons. The separation between the pion and electron peaks is 5.7 ns.A t T w= 143 MeV the results from  two sequences of A (T W,9)  m easurem ents from  the  present experim ent agree nicely w ith each other. T he d a ta  reflect a flat angular d istribu tion  of A(143, 9) w ith values ~  -1.5% . The results from  th is experim ent are, however, incon­sistent w ith those from  an earlier study  a t LAM PF, which consist of values around + 1  to  + 2% in this an­gular region [M asterson et al., Phys. Rev. L ett. 47, 220 (1981), Phys. Rev. C 26, 2091 (1982), Phys. Rev. C 30, 2010 (1984)]. The difference is more th an  can be accounted for by the experim ental uncertainties.The results of the LA M PF experim ent are, however, dependent on the  detailed n ^ p  cross sections th a t were used to  normalize their ic*d  da ta . T heir original valuesTable II. The constituents of the incident pion beam  are tabu lated  at each of the energies studied in this experi­ment. The num bers refer to  the ratio  of particles of a given type to the to ta l num ber of particles of all types. The m easurem ents were obtained using rf-referenced TO F and a 0.6 ns wide proton beam  bucket as discussed in the text.Tn(MeV)Polarity fn U h143 7T* 0.977 0.018 0.0057r“ 0.887 0.011 0.102180 7r+ 0.986 0.012 0.0027r“ 0.942 0.008 0.050220 7T+ 0.990 0.007 0.0027T_ 0.970 0.006 0.025256 7T+ 0.995 0.005 0.0017T_ 0.985 0.005 0.00929of A(Ttt , 9) a t bo th  143 and  256 MeV were based on the d a ta  of Bussey et al. [(Nucl. Phys. B 58, 363 (1973)], used in conjunction w ith the com puter code SCA TPI. Since publication  of the LA M PF CSB pa­pers, there have been several recent 7r± p  cross section m easurem ents published, including one from  this group [Brack et al., Phys. Rev. C 34, 1771 (1986)] which em­ployed techniques sim ilar to  those used in the present experim ent. These new ir^p  m easurem ents were un­dertaken to  resolve discrepancies observed in the  ex­isting 7r±p  d a ta  base. R. A rnd t generated a new set of irN  phase shifts (SP87) based on these d a ta  as well as m any of the  o ther d a ta  sets. The 7r± p  cross sec­tions calculated from  the  SP87 phase shifts were used to  renorm alize the LA M PF data . T heir 143 MeV d a ta  changed considerably, yielding values of A(143,0) th a t were predom inantly  negative and in substan tia l agree­m ent w ith the d a ta  of the  present study. We stress th a t  the  present experim ent is an absolute m easure­m ent of A (T W,9 ) requiring no norm alization to  ir^p  da ta . There rem ains some sem blance of a controver­sial bum p in the  renorm alized LA M PF d a ta  a t about 110 ° bu t it is not sta tistica lly  significant and there is no evidence for such a bum p in the present da ta . T he agreem ent between the  A(143, 9) m easurem ents of th is experim ent and those of the  LA M PF experi­m ent when norm alized to  the  recent 7r± p  d a ta  from T R IU M F shows in ternal consistency between all three of these m easurem ents.T he electrom agnetic p e rtu rba tions which break charge sym m etry are simple in principle, yet there are no m ethods to  include them  exactly in calculations of the sca ttering  of a particle on a com posite system. M ost m ethods make use of the  global param eters C m  and C r  in Eq. (2) as a m easure for CSB. Non-zero val­ues of C m  or C r  indicate CSB. Here, we take the (+ + )  and (+ ) param eters to  be best known. T hen first keep­ing Mo and To fixed, we scan C m  and C r  regions by varying M _ and  T _ . We also consider an alternative To value to  see its influence. The specific combina­tions of param eters we have investigated are tabu la ted  in Table III.Obviously, the  range of inpu t param eters can only be lim ited if the  d a ta  fall w ithin the spread of the pre­dicted A (T W,9)  , and if the spread is large com pared to  the  experim ental uncertainties. These conditions are m et only for Tn= 143 MeV. T he results for A(143,6) are displayed in Fig. 32. T he present calculations w ith C r= 3 .5  or 2.5 MeV all predict positive values of A(143, 9) regardless of the value of Cm - Only the pre­dictions for C r= l-2  MeV produce the negative A(143, 9 >  60°) values observed experim entally. The shape of the  predictions is such th a t  it is difficult to  describe sim ultaneously the  older, forward angle LA M PF d a ta0 20 40 60 80 100 120 140 160 1800 c.m. ( d e g )Fig. 32. The T,r=143 MeV d ata  from the present exper­im ent (solid symbols) are shown, as well as the renorm al­ized older LAM PF d ata  (open symbols). The present cal­culations are shown for C r= 3 .5  MeV (solid curves) and C r= 2 .5  MeV (dashed curves). For a given choice of Cr successively more positive A{Tn ,0) values are predicted as C m  assumes the values 4.5, 3.5 and 2.5 MeV. The dash- dotted  curves correspond to  solutions 7 (upper curve) and 8 (lower curve) from Table III.and the predom inantly  backw ard angle d a ta  of the present experim ent. Given the  problem s discussed above concerning the ir^p  renorm alizations and rad ia­tive corrections to  the older d a ta , we prefer param ­eter set eight from  Table III, which appears to  pro­vide the best description of the  d a ta  from  the present experim ent a t th is bom barding energy, even though the (renorm alized) LA M PF d a ta  are slightly under­predicted.Table III. The resonance param eters used for the calcula­tions shown in Fig. 32 are shown. All numbers are in MeV. Fixed values are M+ + =  1231.1, M+ =  1230.5, Mo=1232.5, r ++ =  111.5 and r+ = 113 .5  MeV.______________________Solution C m Cr M - To F_1 4.5 3.5 1234.9 115.7 113.32 3.5 3.5 1233.9 115.7 113.33 2.5 3.5 1232.9 115.7 113.34 4.5 2.5 1234.9 112 .6 114.35 3.5 2.5 1233.9 112 .6 114.36 2.5 2.5 1232.9 112 .6 114.37 4.5 1.2 1234.9 112 .6 113.08 4.5 1.2 1234.9 115.7 112 .030E x p e r im e n t  378S tu d y  o f  48T i(n ,p )  as  a  te s t  o f  life tim e  c a lc u la t io n s  fo r  th e  d o u b le  b e t a  d e c a y  o f  48C a(R. Helmer, W.P. Alford, Western Ontario)T his experim ent is a test of a specific calculation [Brown, in Nuclear Shell Models (W orld Scientific, Sin­gapore, 1985), p .42] of neutrino  mass. T he calculation was based on the m easured lifetim e lim its for the dou­ble b e ta  decay of 48Ca, and as a byproduct it predicts the d istribu tion  of Gamow-Teller s treng th  in the in ter­m ediate nucleus, 48Sc. Utilizing the well-known cor­respondence between Gamow-Teller streng th  and the cross section for charge exchange reactions at low mo­m entum  transfer [Goodman et al., Phys. Rev. Lett. 44, 1755 (1980)], we have m easured th is d istribution w ith the 48T (n , p )48Sc reaction using the TR IU M F charge exchange facility [Helmer, Can. J . Phys. 65, 588 (1987)]. T he first four ta rgets  in the target box [Hen­derson et al., Nucl. Instrum . M ethods A 257, 97 (1987)] were T i02  powder contained between m ylar foils, and the fifth was a T i m etal foil. A CH 2 ta rget in the fi­nal position provided the cross-section norm alization through the known H (n ,p )  cross section [Arndt and Soper, S cattering  analysis interactive dial-in (SAID) program , phase shift solution SM 86 , V irginia Polytech­nic Inst. & S ta te  Univ., unpublished]. The experim ent was carried out a t 200 MeV, and d a ta  were taken at three angles, 0°, 6° and 12°.Figure 33 shows the results of a prelim inary anal­ysis of the  d a ta  from  the T i foil. The spectrum  wasE> in ‘‘S c  (MeV)Fig. 33. The 48T i(n ,p )48Sc spectrum  at 0°. The dashed lines represent Gamow-Teller strength  extracted from this experiment; the solid lines are from the calculation of Brown.fitted w ith a series of peaks whose shape reflected the known response of the  detection system . T he dashed lines represent the  Gamow-Teller s tren g th  ex tracted  at the given excitation energies. Based on the m easured angular d istribu tion , the streng th  a t higher excitation is m ostly dipole and higher m ultipo larity  transitions. T he solid lines are the  predicted  d istribu tion  [Brown, op. cit.] of Gamow-Teller streng th  based only on one partic le-one hole excitations. I t is clear th a t the calcu­lation fails com pletely to  describe the data . Including m ore com plicated configurations spreads the strength som ewhat from  the single dom inant s ta te  shown here, b u t there is still poor agreem ent w ith experim ent.The spectra  from  the powder targets have recently been ex tracted , and the sum  of all the spectra  have been fitted  as above. The fitted  transitions are shifted in m inor ways in s treng th  and position from  those shown in the figure. A DW IA calculation which will allow us to  estim ate how much nonGamow-Teller s trength  is present in each transition  is in progress.F inal results should be available soon, bu t the m ajor conclusion is th a t th is particu lar calculation [Brown op. cit] of the neutrino  m ass is very likely in error.E x p e r im e n t  379E n e rg y  d e p e n d e n c e  o f  th e  (p, n)  c ro ss  se c tio n  fo r  13 C a n d  15N  (W .P . Alford, Western Ontario)We have studied these reactions in order to  in­vestigate the anom alously large ratios of <Tj,n(0°) to be ta  decay stren g th  for the isobaric analog (ground s ta te) transitions. A ngular d istributions were mea­sured a t 200, 300 and 400 MeV for the reac­tions 7L i(p ,n )7Be(g.s.+0.43), 13C(p, n )13N(g.s.) and 13N(3.51). In addition  angular distributions for 15N(p, n ) 150 (g .s .)  and 150(6 .18) were m easured at 200 MeV and zero degree cross sections a t 300 and 400 MeV.The angle-integrated 7Li cross section has been com­pared w ith radiochem ical m easurem ents [D’A uria et al., Phys. Rev. C 30 , 1999 (1984)] to  establish the mag­nitude of the 7Li(p, n )7B e(g.s.+0.43) differential cross section. The present results establish the 0° cross sec­tion as 35±2 m b/sr(lab ) from  200 to  400 MeV. This cross section has then  been used as a com parison stan­dard  for the 13C ,15N cross section m easurem ents.Zero degree spectra  are shown in Fig. 34. The rela­tively poor energy resolution (~ 1 .2  MeV) arises from the need to  use a well-focused achrom atic beam  for cross-section m easurem ents. T he m agnitude of the 0° cross section is shown in Fig. 35. It is clear th a t the ground s ta te  cross sections and the ratios of ground to  3/2]" cross sections are the sam e for both  targets, and alm ost independent of energy. T he slight energy31230200130i o oW 30 ^  BO OOO  BO OO *cL_(D 200 -Q ^ 300 C 230 200 130 IOO  SO O300-i3.3 113n200i / v k .  :o»3 . 3 1300 M«V■«•0  1 0 0i , . . i400-cncDoo<D_QEDCFig. 34. Zero degree spectra for the (p, n) reaction on 13C and 15N at 200, 300 and 400 MeV.300 M«VB . IB* 4 - 0 0  M ® V4-00300200IO O♦ o o330 300 230 200  -  130 - IOO - 30 - 230 -b-o. 10*10 15 20 25 30S  (deg)10 15 20 25 30 356m (deg)C-O # \ 10# b •o9round stateM 1 M«V (« » )  13^J200  MeVFig. 36. Angular distributions for the (p , n) reaction at 200 MeV leading to the ground sta te  and 3/2J" sta te  of 13N and 150 .  The solid curves are the result of DWIA calculations.32Fig. 35. Energy dependence of zero degree cross sections for the (p , n ) reaction to  the ground sta te  and 3 /2 f  sta te  of 13N and lsO. The cross-section ratio  is shown in the lower panel, along w ith results of a DW IA calculation.dependence observed for the ra tio  does not agree w ith th a t predicted for 15N using a DW IA calculation w ith Love-Franey in teraction  [Franey and Love, Phys. Rev. C 31, 488 (1985)].A ngular d istribu tions for the two targets a t 200 MeV are shown in Fig. 36. The solid curves are DWIA calculations using em pirical optical potentials, Cohen- K urath  wave functions [Nucl. Phys. 73, 1 (1965)] and Love-Franey in teraction  [op. cit.]. T he forward angle cross section is well reproduced for ground s ta te  tra n ­sitions, bu t the  DW IA result is too large by about a factor of 1.7 for the Gamow-Teller transition  to  the 3/2j" s ta te . T his is consistent w ith the usual quench­ing of G T  transitions observed in (p , n) m easurem ents [Goodman and Bloom, in Spin excitations in nuclei, ed. Petrovich et al. (Plenum , New York, 1984), p. 143]. I t  is also clear th a t the  DW IA curves fail to  fit the  angular d istribu tion  shapes a t angles greater than  about 10°.Further calculations are being carried out in an effort to  identify the source of the discrepancies between the current calculations and the m easured cross sections.E x p e r im e n t  381M e a s u re m e n ts  o f  s p in  o b se rv a b le s  u s in g  th e  [p ,p 'l)  r e a c tio n(K. Hicks, TRIUMF; J. Shepard, Colorado; M. Kovash, Kentucky; N. King, Los Alamos)E xperim ent 381 m easured the (p,p'~f) reaction on 12C a t 400 MeV a t pro ton  angles between 6° and 13°. E ight BGO 7 -ray  detectors were placed in plane a t an­gles spanning -90° to  +90° and two B aF 27 -ray  detec­tors were placed above and below the target. Proton singles were recorded sim ultaneously w ith the coinci­dence events w ith a known prescale factor. A short run w ith a 6Li ta rg e t provided a calibration from the 7 -decay of the 0+ s ta te  a t 3.56 MeV to  the 1+ ground state.The results for the 6Li calibration run a t 6°, for both absolute cross sections and analysing powers, are pre­sented in Table IV. T he 7 -ray  coincidence cross sec­tions for 6Li show the isotropic shape expected for this transition . These cross sections have been corrected for detector efficiencies from  M onte-Carlo sim ulations based on the excellent agreem ent between the 7 -ray pulse-height spectra  and the shapes (and m agnitudes) calculated w ith the M onte-Carlo code. Similar efficien­cies have applied to  the  12C coincidence cross sections for sim ulations run  for 4.44 and 15.1 MeV incident 7 - rays.T he proton singles cross sections for the 15.1 MeV 1+ sta te  in 12C are found to  agree (w ithin errors) a t all angles w ith previous m easurem ents m ade a t LAM PF. The 7 -ray coincident cross sections and analysing pow­ers for the sm allest and largest p roton scattering  an­gles of the  present m easurem ents are shown in Fig. 37. The angular correlations (top) show the characteris­tic shape of A  +  5cos(207 ) +  Csin(207) expected for a 1+ to  0+ transition . T he theoretical calculations shown in the figure com pare relativ istic  and nonrel- ativistic models th a t include explicit exchange. The angular correlation d a ta  favour the  relativistic model for the  larger pro ton  angle shown in Fig. 37. The analysing powers are no t in good agreem ent w ith ei­ther model. This is also seen for b o th  proton sin­gles and polarization  studies for 12C a t 400 MeV, as shown by T R IU M F E xpt. 324 results. D ata  for the 4.44 MeV 2+ s ta te  are also available (bu t not shown), and are in good agreem ent w ith the relativistic calcu­lations (bo th  angular correlation and analysing pow­ers).The basic theoretical framework for the  calculations shown in the figure are discussed in a preprin t by J. Shepard a t U niversity of Colorado. T he (p ,p '7 ) ob­servables are shown to be sensitive to  specific parts33T able IV . E x perim en t 381 resu lts . 6L i(p ,p 'y ) E x =  3.56 MeV (0+ ), Tp =  400 MeV.ecPm-(deg)dcT/<mcp m- (m b/sr)Ay 0’7ab(deg)(<hr)/(dO‘ 'm')/d f]!yab(m b /sr2)a c o in cJ\y7.36 0.816(15) +0.04(3) 87.6 0.071(1) +0.01(4)116.5 0.068(1) +0.05(6)143.5 0.069(1) +0.05(5)166.3 0.070(1) -0.02(5)194.0 0.071(1) -0.01(5)217.1 0.069(1) -0.02(5)245.0 0.070(1) +0.05(5)272.9 0.071(1) +0.07(4)top +0.09(3)bottom +0.03(4)of the proton-nucleus in teraction th a t are not avail­able from  other m easurem ents. Similar calculations for ( p ,p ' j )  m easurem ents from  IU C F have been sub­m itted  for publication. A full analysis of the present m easurem ents com pared to  calculations is expected by February 1988.Fig. 37. 7 -ray coincident cross sections and analysing powers at proton angles of (a) 6.7°, (b) 13.3°.a).15 DREX (relativistic model) DW81 (nonrel. model)“CCp.p’y )  400 MeV 1+ (15.1) Q =6.7°DREX (relativistic model)---------- DW81 (nonrel.34E x p e r im e n t  382M e a s u re m e n ts  o f  th e  s p in  r o ta t io n  p a r a m e te r  Q as a  te s t  o f  P a u li  b lo c k in g  in  p ro to n -n u c le u s  e la s t ic  s c a t te r in g(0 .  Hausser, SF U /TR IU M F ; M. Vetterli, SFU)M easurem ents of the spin ro ta tion  param eter Q have been very im portan t in the  developm ent of relativis­tic (D irac) theories of elastic scattering. F irst it was found th a t phenonomological fits to  cross section a  and analysing power A y using relativ istic  dynam ics were ca­pable of predicting Q; the same was not true for phe- nomological fits using nonrelativ istic  (Schrodinger) dy­namics. Next it  was shown th a t a t energies above about 500 MeV all three elastic scattering  observables could be reproduced using the relativ istic  im pulse ap­proxim ation (RIA ), folding the free nucleon-nucleon ( N N )  f-m atrix  w ith the ground s ta te  density. How­ever, when th is same form alism  was applied a t lower energies (~200 MeV) the agreem ent was not nearly as good. T he poten tia ls predicted by the RIA were much deeper th an  those found in phenom enological fits. This problem  was u ltim ately  traced  to  the param eterization  of the N N  f-m atrix , where the %N coupling was taken to  be pseudoscalar ra ther th an  pseudovector. On the energy shell, i.e. for N N  scattering , both  pseudoscalar and pseudovector coupling give the  same scattering  am plitude. However, when used to  produce nucleon- nucleus optical po ten tia ls the  pseudoscalar coupling results in po ten tia ls whose depths diverge as the en­ergy goes to  zero. Pseudovector coupling, on the other hand, gives po ten tia l depths which are roughly con­stan t for all energies, in much b e tte r agreem ent w ith the phenom ological fits.Horowitz and M urdock improved on the RIA cal­culations a t low energy by (a) using the pseudovector n N  coupling, (b) using a param etrization  of the N N  f-m atrix  th a t includes explicit exchange, and (c) in­cluding Pauli blocking. These calculations, when com­pared to  the  E xpt. 294 Q m easurem ents on 208Pb at 290 MeV, h in ted  a t the im portance of the Pauli block­ing m edium  m odification a t low energies. Experim ent 382 proposed to  m easure Q a t 200 MeV where Pauli blocking effects are expected to  be more im portan t.A m easurem ent of Q  involves scattering  a sideways polarized beam  from  the  ta rg e t and determ ining the angle th rough which the spin ro tates in the  scattering plane. T he present experim ent was perform ed on beam  line 4B using polarized protons from  the T R IU M F cy­clotron. The norm al (h) polarized proton beam  was ro­ta ted  to  sideways (s) using a superconducting  solenoid ju s t upstream  of the in-beam  polarim eter (IB P) on line 4B. T he polarization of the beam  was continu­ously m onitored using the IBP. T he polarization of thescattered  protons was determ ined using the focal plane polarim eter (F P P ). T his polarization comes from  the ro ta tion  of the  incident sideways polarization  and from an induced polarization  P .  T his induced polarization is the  same as the  analysing power for elastic sca tte r­ing. Since the F P P  comes af