MOMENTUM AND ANGULAR DISTRIBUTIONS OF CHARGED SECONDARI'ES IN 40 GeV jc

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1 ОбЪ8АИН8ННЫИ ИНСТИТУТ ядерных исседваним дуби а El84442 MOMETUM AD AGULAR DISTRIBUTIOS OF CHARGED SECODARIES I 40 GeV jc я А ITERACTIOS WITH SIGLE PARTICLE HIGH pj TRIGGER Berl inbudapesdubnapraguesofiatbilisi W arsaw Collaboration Submitted to XXII International Conference on High Energy Physics (Leipzig, 984)

2 ,, i, ITRODUCTIO Investigation of processes with high Pi particle production in hadronhadron and hadronnucleus interactions is of big interest for hihenergy physics because а new information about hadron structure and pacetime picture of hadron formation is expected to Ье obtaiцed As yet almost all the data are inclusive or semiinclusive BubЬle chamber results refer to the Pi region below 2 GeV/c However, it is for Pi > GeV/c where the change in the dependence of differential cross sec tion versus transverse momentum is observed 2 (transition from exponentiallike behaviour to powerlike one) Furthermore the anomalous growth of cross section with ma ss number А has been found for Pi region of 2+3 GeV /с in hadronnucleus interactions (Cronin effect) 3!, It has no satisfactory theoretical explanation as yet ew experimental data of exclusij e nature are needed to continue detailed study of higi Pi processes EXPERIМETAL ( SETUP The experiment has been performed with RISKspectrometer 4 where interactions are detected in а 5meter streamer chamber Tie streamer chamber technique allows us to investigate rare processes (cross sections below Ь) at nearly 4 eometry with high multitrack efficiency The sketch of experimental seup is shown in Fig Unse parated 38 GeV/c beam of negatively charged particles (98%, 7% К and О 3% р ) produced from interncll target of 70 GeV proton synchrotron (Serpukhov) was focussed onto the target placed inside the sensitive volume of the streamer chamber Н 2, D2, С, Cu, and РЬ targets were used Charged high Pi particles were detected with telescope of three twocoordinate multiwire proportional chambers Dimensions of sensitive areas of chambers were IOxOS m2 (horizontal and vertical, respectively) The clamber telescope has been placed above the streamer chamber in nonzero magnetic field region and covered the polar anle interval 2 < (} < 22 for particles originating from the target (it corrёsponds to 85 < (}* < 20 in cms) Fast processor, using ИWPCinformaton, selected events with charged particle having Pi above predeterminated threshold This threshold has been varied from 0 GeV/c to (#(!;, :, \,!JШt:Z:Ii БЧЬJI а: i t J Jii:B:itrel > г: \! ::

3 , ill<! >j, :\ v t;l + 8 =! f\ \ \ t;;l Е: <tj l\) А + =! л ::! Ei 0\J :!> [ Q f\ с r г t::j, ё с::;;::: _,,, <tj =! Щ!fJn ;{JDJI_IQJO t;l f\, =! _r:_:_; + RESULTS AD THEIR DISCUSSIO :! \ \,Qtj t:}) >,, :n ff,, tj,> J\ o <+,!> \,, t)!j :::: t::: а:: <tj CJJ З) 5 GeV/c, Trigger acceptance was 6% in PL range from threshold to 25 GeV/c >::S, F + + \ \ ;,) А л :7) + + =! + r s:: \ 7 2 \ =! Q) Cl! r s:: \ 7 Л р Pi l:; t::; \ i j!>!> t С) s i е j In this paper the data obtained from full reconstruction of 500rтС and 500rтРЬ events are presented, Target thicknesses were 9% and 0,7 % of nuclear absorption length for carbon and lead respectively, Events to Ье measured were selected Ьу film scanning with rrnтcinformation taken into account, During the scan procedure tracks of highly ionizing particles ar registered visually, All secondary tracks we re measured in selected events and reconstruction of momenta and emission angles was performed Ьу а computer pro gram, Hi ghly ionizing positive particles with momenta below 500 HeV/c were identi f ied as protons Some characteristics of events with triggering particle having transverse momentum above 3 GeV/c are shown below In Fig2 transverse momentum distribution s of secondary charged particles are dernonstrated with identified protons being exclud e d The sl ope of PL spctra of associat e d particles is steeper for РЬ target than for С target Hence, the average transverse rnornentum, PL >,of the s e particles is less in рь than in 77с events Compari s on wi th nonbiased ine lastic 77с 5 and 77рь interactions (see the ТаЬlе) showed that <PL > of particles associated with high PL tri gger is hi gher for carbontarget and do not differ for leadtar get One can see also rhe difference between rapidity distributions of 77с and 77рь events with highpl trigger (Fig3): the nurnber of particles produced in the target fragrnentation region is larger on Pbtarget than on С target while in projectile fragrnentation region the relation be tween nurnbers of secondaries from two tar gets is reversed The c enter of rapidity distribution for 77с interaction is shifted toward the tar get fragrnentation side in cornparison with nonbiased inels tic events and the rapidity spectrurn is mor e narrow for high events, The excess of positive charge of fast (Р аь О 7 GeV/c) particles, QF = n+ n, d i ffers significantly for РЬ and Ctarget Within sta tisti cal e rrors Qris oofor carbon while for lead it equal s 29+0,3, All th e se fact sappear to indicate that rnultipl e scatter i ng of hadron constituents qr of e ntire hadron in nuclear rnatter con tribute s significantly to hi gh particle production on he avy nuc leus Within s uch rnodel transverse mornenturn o f tri ggering particle can Ье cornpensated Ьу а few particles with rel a tively l o,, PL Hence, the average PL of associated 3

4 rrc },::rotms,, г JJJ:J dy 00 Fig 3 Rapidity (У аь) distribution ( protons) Triggering particle rapidity is equa l t o 2 тr с тr РЬ ipb r : L r particles should нt increase in comparison with nonbiased ine la s tic collisions and the excess of positive charge of fast par ticles appears For li ght nucleus such mechanism should Ье less important Due t o larger statistics of selected rr С interactions it was pos s iьle to study events where trigge ring particle had higher PL momentum (>5 GeV/c), One can expect that some interaction features should appear in such events more clearl y In Fig4 distributions of azimuthal angles between triggering particle and all associated secondaries are shown, An increase of az imutha l correlations is observed at t 80 in the centr a l int e raction region (i tyl, ty difference of rapidities of associated and trigge ring particl e) whereas in the targe t and proj ec tile fragmentation re gi ons no such correlati on is presented The con tribution of pion c resonances to hi gh PL particle production was estimated in rr С events with tri gge ring particle having PL 5 GeV/c Peaks of р 0 and fmesons are clearly seen in the spectrum of + combinations of tri ggering and a ssociated particles (Fig5), About 25% and 5 % of triggering pa rticles with Р 5 GeV/c origin from р and f decay respectively Similar spectra for triggering particles with PL,3 GeV/c on РЬ and С targets do not show resonances clearly It can Ье expected that increasing of statistics will allow one to study multiple resonance production, 2 Jl 2 УLаЬ тгср >5 GeV!c /fjy/ < 60 5О Fig 4 Azirrтuthal correlations between triggering particles ( PL 5 GeV/c ) and all associated secondaries for rrc interaction in thr ee ty intervals ( ty diff er ence of the rapidi ties of associated secondary r and triggering particle) 4а the central r egion $ to,y $ ; х like( ); unlike (; +); 4Ъ t he fragmentation r egion of incident rr ty ; 4с the target fragmentation r egion ty < r >,/ I, / /,_!;х : Г :J(} 20;,:: а {fio il ю lidifl 9d fjy > : О fjy< _ :i : О _, ь REFERECES, Alper В et al PhysLettB, 973, vol 44, р52; ucl PhysB, 975, vol IOO, р237; 976, vol,4, pl 2 Busser F W et al uclphys,b, 976, vol I06, pl 3 Cronin J,\, et al PhysRev, 975, Dll, р305 4 Andreev ЕМ et al Journof ucl Phys, 982, vol35(3), rajfl 90, / / 0 I с р Angelov et al Journof ucl,phys, 977, vol25(5), p IOI3, Fig 5, Spectrum [ efferjtive masses rr rrin the combination of triggering particl and associated secondaries J Received Ьу PuЬlishing Department on June 26, 984, 5

5 Адам Д и др Е Импульсные и углаые характеристики заряженных частиц в лвзаимдеаствиях при 40 ГэВ/с в бытиях с рждениен адрна с блымим пперечным импульм Плучены углвые и имnульсные спектры, распределения п быстртам и эективным массам втричных заряженных частиц в си рьвзаимдейст виях при импулсв 38 ГэВ/с с триггернй частицей, имеей пперечный им пульс Р ГэВ/с и вылетащей в системе центра масс rr системы пд угла ми 8*85 20, Пка3ан, чт средние пперечные импульсы втричных адрнв в неупругих,рьи свзаимдействиях и асциирванных адрнв в прцес сах с бразванием частицы с бльwим пперечным импульм впадаqт для свинца И несклк раэличаqтся для углерда В бытиях с бразваниен части цы с бльшим пперечным импульм на мишени из свинца наблqдается увеличение избытка плжителн заряженных частиц с импульм PJ 0,7 ГэВ/с п срав нениq с данными на миени из С Эти акты свидетельствуqт в пльзу механиз ма бразвания частиц с бльшим Р за счет нескльких перерассеяний внутри ядра Пказан, чт в свзаимдействиях значительная для час т иц с бльшим пперечным импульм присхдит т распада р 0,+ Рабта выплнена в Лабратрии ядерных прблен ОИЯИ Преilриит О!tlедивеввг ииститута J!Дерных исспедваиий Дубна 984 Adam Gy et al, El84442 Нomeпtum апd Angvlar Distributioпs of Charged Secoпdaries iп 40 GeV/c wa lnteractions wi th Single Particle High Р Trlgger Нomentum and aпgular spectra as well as rapidity and effective masses distrlbutlons of charged secoпdaries in 30 GeV/c с and рь interactions triggered on а slngle particle emitted at н cms angles with transversal momentum PJ GeV/c are obtained l t is shown that the average transversal momenta of secondary pions for inelastic interactions апd pions assoclated to the hlgh Р& partlcle coiпc i de for the РЬ target and are sl ightly dlfferвnt fг the Ctarget lncrease of the excess of pos i tively charged partlcles havlпg momentum аьvе 0 7 GeV/c in high PJ processes п the Pbtarget ln compaгlsoп with the Ctarget is observed These facts suggest the multlple scatterlпg mechanism of the high Р& partic) e production п nuclel lt is shown that а coпsideraыe part of tr iggering particle iп с interactlons origiпates from р 0 +decay The investlgatlon has been performed at the LaЬoratory of uclear РгЫ erns, J ltir а Preprint of the Joint Institute for uclear Research DuЬna 984