High Energy Electroproduction and Spin Physics
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SLAC-392 SLAC WORKSHOP on HIGH ENERGY ELECTROPRODUCTION AND SPIN PHYSICS February 5 - 8, 1992 Prepared for the Department of Energy under contract number DE-AC03-76SF00515 STANFORD LINEAR ACCELERATOR CENTER Stanford University • Stanford, California DiSTr ijIijr.'ON Of 7fii» DOCUMENT !S UNUMiTEC This document and the material and data contained therein, was devel oped under sponsorship of the United States Government. Neither the United States nor the Department of Energy, nor the Leland Stanford Junior University, nor their employees, nor their respective contractors, subcontractors, or their employees, makes any warranty, express or im plied, or assumes any liability or responsibility for accuracy, complete ness or usefulness of any information, apparatus, product or process disclosed, or represents that its use will not infringe privately-owned rights. Mention of any product, its manufacturer, or suppliers shall not, nor is it intended to, imply approval, disapproval, or fitness for any particular use. A royalty-free, nonexclusive right to use and dis seminate same for any purpose whatsoever, is expressly reserved to the United States and the University. 2/80 SLAC--3 92 DE92 011077 SLAC WORKSHOP on HIGH ENERGY ELECTROPRODUCTION AND SPIN PHYSICS February 5 - 8, 1992 Stanford Linear Accelerator Center Stanford University, Stanford CA 94309 Prepared for the Department of Energy under contract number DE-AC03-76SF00515 _. Printed in the United States of America. Available from the National Technical ilJjsV • ™" Information Service. U.S. Department of Commerce, 5285 Port Royal Road,Springfield, Virginia 22161 ;K PREFACE 2. Hnvv many f|'i.irk.'- and 'o: I*IIII>II=. p.irttf'ipnle m p,»rti* isl.ir reaction'; ai Iiu-h eneri'.j" 1 ,). \\ fi,tl i ,u:ii'' ;;I.- ijtji ]eiyii ,s|)j[| the V,\[i in, r (L'l.uk -. th<- un-i)n iriark).. the These IVoc-c^dtriiis wuin ono<« M the traw-parciKies prt'scEitrn1 ai the Work shop on High Energy Elect rupruduct ion and Spin Physirs held a-t SI AC on Febru ary 5-3. 19(J2. The purpose of this Workshop WH to bring, people together lu discuss •I Wliat lupin-ii-. to thr liu.--l»-ori fragment;, after a hard colhrHvn*' the possibilities for new experiment* u;ing the SI.AC ni^b intensity electron and i (("«.' doe^ tli- imr |-'ar nifliiiiinharifie 'he answer* to any ijf these question!.'' photon beams and the facilities of End Station .4 These iiur>lii>ji- ate all interrelated, and t|i- anvm-r* will only come from the- Recent development* made this an opportune time fur such A workshop. The combined evidence frrmi many different rn«lA.4ure«x-iil*i. Wruti ^w^Av-il \»is Work primary motivation was the increasing interest in the piiysirs of tjL'D structure shop IN the grmvini; understanding in the ph.i'.icv community that thf facilities* at of nue'eons ai:d nuclei for which the SLAC beam and experimental facilities are ?!.AC ntfef the id-.u liKih i"t studying lh*-.e is.ue- The primary advantage nf the ideal tools. Much i* known &hciui tin- quark structure of rmck-ons after more FI.AC is the av;ulaUi.t> ,-if vcry Jngli inler.-Jlj br,ims (.u.il aLo sotiti high elect;.in than 25 years <if in<-'PitiRMioni.. but murK moif remains to W leajnu'd. For exam polan;.Ji<Mi) in jwr-nsely \\tf eni'rijy rangf nn'di'ii to siudy these phviiomeria. U'e ple, we. now know taiil>' well the basic features of tin- quark and gluun momentum knuw from A Uaaf hudy uf d;ita. tlat \\\ \\»- region bt*:wwn a few OV and a f.-w distributions. The flavor structure has been partially n:aj>jjcd out with neutrino tens of (JeV m etier,;y or nionientuni transfer liiere is a iransitiori frotn the nif-sun- beams. The most recent generation of precision dee.p mela&Eir electron and muon nutlruii pictnrr v.h».fe the whole hadrun parHi"ip-it<-- in any reanion. (o ihr ci,tiArk scattering exp.'rjniepla ha$ yielded a largie and mostly tftiiliislenl rfjta set spanning seal t rt K ri'KlOli. when' rrariioli'* tatic ]>larr j>rrdommanr)y u;i a few allJark^ an • I/or & wide ra.nge in Q* and lijorken x that has recently been used for the first reli (jltion?- At ener^v nr momentum transfer higher than '.ill I" 50 CeV. ivpiral r,f tEn- able extraction of next-to leading order (higher '.wistl coiitribntinrii.. Electron a.nd muiiii siMitenng e\(..,•^ir^1ent^ at Fermi lab and ("F.KN i.tr example, tin- iiwlti<viAfk mil or. scattering, together with /i-pair production, on heavy nuclei have yielded a nature of the tarcet i? io*t and only the purely p*:rti.irS.*,in.e QCT> plienortiena seem mnsistent picture shoving subtle diaiiirtinus of i\ir quark momentum distributions i»i lurvive. Knef(5ies,of ihrt-.- v& four OA", -suon l./ be available a: CLBAf- are not in nuclei (called the EMC effect), but there is little r-.a! undciUandiag of the ori high eiiomsh in piol/e the suaJing regiuii SLAC is the best place to study the gins of litis phenomenon in QCT3. The list uf places where, we have begun to see multitude of pheiiujueiia that occur at ih>- <.n\^'\ cf sralmg- the behavior of the underlying quarks and gluons MI hadromr structure is long and has been growing in rermt yv*rs. However there art? still fundamental problems Many uf the rea. lion.i we wuuld likf \^> meaj-urf hav small cr-vs; i.-ciiur:* that and puzzles ra^ed by the present data that remain tu ue, solve J, can iKily he ob-1'Tk..d using a conibinaumi of tujtt; beam cimem-i, ;hu^ taryen,, apd well designed spectrnmett'fs and denr< toi vystrm1 ilia: can filler out the largje The main problems can he Mimmarized by the following liai of simplified ques flitx of mi wanted h.ti l.u.'Kmwi i>MMclt^, TW *s\CT«vr ami rea.\i\y aiiapl(ibi»« nper tions one might a.sk j.bimt aucleon structure ami reaeiton.s on them at high energy. trometer and heainhne facilities of End Station A c.in be a:raii(r.>d in a variety nf fflnfiiiurdiiiJi-. t" >UJ! the ^fieuali/ed :ni-d- -'i a A'idr r.iritf'' uf '•vpe.mi-fdt.s \. How is tin- miKTH'iUuirj <Ji*lnb'ited atrioung the rui' h-mi tons; mints'.' itrcmt rtt'Vclu[j|ur;ns in ii'rhniijia** fur making ptAt\ttv.ed beams and targets aprciro-meter. (>x d'-letlor capabilities haw stimulated verv string interest in a. new gem-ration of fixed target experi • Descriptions of ^ssible future «p«;niw!nts to addict particular physics ments at SLAC tti.u off'-; exciting possibilities f»»t major advances in nrusuKJiients question of nudeon spin .iLrurlucc. A n<;w generation of pnlamed proton and druteron tar The topics and speakeu ar*- all given in the Workshop Agenda in the following gets made of ammonia with high poUrization, rapid polarization times, ,»nd high pages, and the individual presentations are here for you lo review. We decided to resistance to radiation damage are now being buiit. They will yield an gcder of present the speakers' transpirenciev rather than produce a. more formal proceedings magnitude increase in maximum luminosity over similar targets of a. d«id<- ago. 50 that the results could be qnj«-kly available to the community in keepiiig with the A new technique is uow being used At SLAC to make a target which is effectively spirit of a Workshop- In the list flexion. Prof. Mark Strikinan gave his summitry of polarized neutrons by producing polarised SH« «?ing 'jplical pumping and spin the Workshop and his personal answer to the. question "What &tc the high priority exchange from Rh. hi a very interesting recent development a.t SLAC, specialized experiments for which SLAC is tmiriueiy suited and which will be feasible in the photo cathodes ol iiiultilnyprcd materials, have Wn made UJJII, in the present early near fature--*1 He listed ae«*cn bis;h priority experiments, and ffivm thiec of them a stages, are producing electron brains in icsls with 70% to S0% polarization and "gold plated" rating While 'ui>. priorities may n»t agree with youra, it is e\e\t that L:ioiigh intensity lo be useful fur End Station A beams. This is an increase of a the potential future experiments could provide key flvidenrc needed to answer the factor of two over tlje pi/Urisatiun achievable from pliuto cathodes made from bulk open physics questions. materials. A factoi of two increase in polarization gives a factor of four increase The forthcornir.g measurements of jiur!eun spin strurturc in the already ap in tlie sensitivity of tbe experiments. It looks promising that within a. year o: 50 proved experiments El-15 at>d EM3 will be decisive in helping to resolve lbs "spin it will be passible 10 us-.- tlic iimv cathodes in an eleruun gun to produce bighEy crisis" presently evident ir. itr SLAC/tMC spiu structure measurements c.n th* polarized beams fur Fnd Station A. proton. The wide range actoMtne in i,*spetia'!y *"ith tbr rifl C*:V beitn. logethfi On top of the already exlemive exiling SLAC infrastructure (lirjac. A-lme, with tb<- tight control over systematic rrtois that is athievable with the bigb lumi End Statk'ii A, spectTorneUTi. detectors) there is ncm- in the planning stages a nosity and high polarisation at SLAC. wili yield a crucial (est of the Rjork^n sum significant upgrade of the facilities thai would allow beam energy up to 50 GeV rule l0 the 10% level to he delivered in rid ^latiun A.