И Ф В 3 ПЭФ PARTICLE PRODUCTION BY 70 GeV/c PROTONS. Serpukhov 1975

Transcription

1 I N S T I T U T E F O R H I G H E N E R G Y P H Y S I C S И Ф В 3 ПЭФ Yu.M. Antipov, V. A. Bessubov, N. P. Budanov, Yu.B. Bushnin, S.P. Denisov, Yu.p. Gorin, A.A. Lebedev, A.A. Lednev, Yu.V. Mikhailov, A.I. Petrukhin, S.A. Polovnikov, V.N. Roinishvili, V.S. Selesnev, V.I. Sergienko, D.A. Stoyanova, A.N. Sytin, Ya.A. Vazdlk. F.A. Yotch PARTICLE PRODUCTION BY 70 GeV/c PROTONS Serpukhov 1975

2 Yu.M. Antipov, V.A. Bessubov, N.P. Bubanov, Yu.B. Bushnin, S.P. DeniHOv, Yu.P. Gorin, A.A. LebedeVj^^jftu.. Leclnev, Yu.V. Mikhailov, A.I. Petrukhin/jfi.A. Polovnikov, V.N. Roinishvili x, V.S. Selesnev, V.I. Sergieriko +, D.A. Stoyanova, A.N. Sytin, Ya.A. Vas:dik+ F.A. Yotch T/<A PARTICLE PRODUCTION BY 70 GeV/c PROTONS Lebedev Physical Institute, Moscow. к Iastitute of Physics, Tbilisi.

3 M--4 Аилтов Ю Л, Беззубо» В.А., Буданов НЛ., Бушиив Ю.Б., Вазшж Я Д., Горин ЮЛ., Донисс» С.П., Еч Ф.А., Лебвпив А.А., Леднев А.А., Михайлов ЮЗ., Петрухин АЛ., Пояовинко» С.А., Ройкашвши В.Н., Селезнев B.C., Сергиеяко В.И., Стоянова Д.Д., Сытив АЛ. Образование J/(& чветжпы цротошмж с импульсом 70 ГэВ/с, Серпухов, стр с рис. (ИФВЭ ПЭФ 75-!S). Библиогр. в. В работе првястаплевы результаты змерекий спектра,<ф<{»кгивн1ах масс мюонньи пар, обрааонаннья протовамв с имвулъсом 70 ГэВ/с в бернллиевой мишеин. В спектре отчетливо проявляются пшш, расположепные в обпаста масс р-ш и-мезонов, Ф-мезова и 3/4 -частишы. Анапно событии в области лиха 3,1 ГэВ позволил получиъ кнклюзивнъе р»опр«де;юнмл J / ф -частно по рр, перемон- юя Фейнмана х и бьстроте у*. Полное сечеише реашош р + Be ( J/(d- fi + /Г) +... оказалось равным 9,5.,5 нб>1/ г яяро Во. AbBtmct Antlpov TU.«., Beeiubov V.A., Budanov M.p. Bunhnin TTu.E., Denleov S.P., Gorin Tu.P., Lebedev A. A., Lednsv A.A., Mikh»Hov Yu.V,, Petnikhin A. I., Polovnikov S.A.. noinlshvili V.N., seleenev V.S., Sergienko V, t,, Stoyenovo D,A., Sytin A.S,, Vazdil; Y«.A., Totch P. A. 3/Ф Particle Production by 70 GeV/o Protons. Serpukhov, p,. (IHKP 75-15). Ref. 8, Invariant muss epectru» of p.* \T pairs produced by 70 GeV/c protons In Be tarcet RTQ pree&nted, Difftlnct enhancenenta in the паве roglons of p, to mesons, ф meson end J/Ф ptsrticle жхо obaarved. For 3/Ф production, x, y* and p* dletrlbutiono are Riven. The total аговв aeotion for the reaction p + Be -»(J/ii>- ц * i -) *... is equal to Я.5 ± + Z,5 nb/nucleui.

4 This paper describes the measurement of dimuon production by 70 GeV/c protons in Be target. The goal of the experiment ms to study the production of з/ф and other resonances decaying into f» + (i~ pairs. The experiment // beam of the ihep accelerator " /3/ spectrometer. was performed in the positive using the apparatus of "Sigma" 1. EXPERIMENT At. LAYOUT AM) EQUIPMENTr The layout of the experiment is shown in :fig. 1. The 70 GeV proton bean incident on the target T was defined by scintillation counters s, - S_ and A. Beam Intensity used was 8.5 x 10' pps. Small scintillation counters S_ and S o detected about 10% of the 7 о total Intensity and were used to control the deadtime losses of the beam monitor. The direction of incident protons was measured by scintillation hodoscopes H (11 elements 8 x 8 nm ) end И 1

5 FEBRUARY p APRIL MAGNET ABS ABS I..!. /l/jl // \/ \- H, Pig. 1. Layout of the expor latent el equipment l:i February and April run». S - S g, А, В, г.. - R f, 0: scintillation counters; Hj - H«: hodoecopes; T:Be target, alternated by scintillation counters: PC: proportional chs»ber; sc o - SC 5 : wire spark cnambers; ABS: 1 и steel absorbers.

6 (5 elements 5x5 nun") with an accuracy of ±0. mrari. The beam size at the target was cm wide and 3 on high. A 36 cm long Be target T was alternated by eight tion counters with the dimensions )!0 x 80 x 8 mm. The pulse height analysis of signals from these counters was used to determine the interaction poinc. During some runs я scintillation hodo scope И, proportional chamber PC and 00 g/cm** carbon absorber were put just behind the target. The particles leaving the target, in the forward direction, теге bended by the magnet M and detected by the scintillation counters Rj - R., Q, wire spark chambers SC and scintillation hodoscopes И, H. The spectrometer megnet M bad an effective length 4 5 of 3 m and a field integral of 45 kgm, The magnet aperture, which was 0,7 x 1,6 ra, determined the acceptance of the spectrometer. The dimensions of the R counter and quadrant Q were x 1 m and x m, respectively. The quadrant Q consisted of 16 scintillation counters, combined into two groups:rh group Q and LH group 0. The wire magnetostrictivo chambers SC contained four coordinate planes each with the dimensions 1.6 x 1 6 m. The elements of hodoscopes H. and Hg were 10 x 10 cm. The 1 m steel absorbers ABS were used to identify muons. The scintillation counter В detected protons, that passed through the target without interaction. The scintlllao signal S.- ABRj.,4 0 Qj was used as a trigger. This signal indicated

7 that proton hit the target, as a result charged particles that had passed 3 m steel absorber, appeared in the KH and Ш parts of the set up downstream the magnet. The information from the chambers, scintillation counters, hodoscopes, quadrant and pulse height counters was recorded on magnetic tapes. The experiment was carried out in February-April Before the April run was started, the geometry of the experiment had bsen changed in order to increase the acceptance of the spectrometer (see figs. 1 and 8>.. DIMDOir EFFECTIVE MASS SPECTRA The events which satisfied the following requirements were selected for analysis: 1. Hodoscopes Л andit detected only one particle. 1 «. Pulse height counters showed that interaction had taken place in the target.the vertex determined by pulse helg-ht counters was used to calculate particle momenta. 3. spark chambers SCg_g detected at least one positive and one negative "muon" tracks. The track was considered to be a "muon" track, If sparks were observed in all four planes of the chambers SC. or SC and the distance between these sparks and track extrapolation was less than three standard deviations expected from multiple scattering.

8 1. Muon momentum is greater than 5.5 GeV/c. 5. The vertical projections of the tracks for ц + and V~ mesons and incident proton crossed at one point, and this point is within ±0.5 ra from the target unit, where» interaction occured. Dimuon mass spectra for selected events are shown in fig. (with carbon absorber) and fig, 3 (without carbon)*'. In both spectra one can clearly see enhancements in the mass regions of p and w meson, Ф meson and J/Ф particle. Below some results on studying м + ti~ production with effective mass M> GeV are presented. The dimuon events with p ^ ^ 55 GeV/c and p.$1.5 (GeV/c) were used in this analysis. 3. INCLUSIVE DISTRIBUTIONS FOR j/ф PRODUCTION Dimuon mass spectrum measured without a carbon absorber is presented in fig. 4 in semilog plot. The spectrum decreases exponentially from.0 to.9 GeV. Extrapolation of this dependence into the region M >.9 GeV shows that the background level at 3.1 GeV Is about 6%. For measurements with carbon absorber the background level is ^3%. For events with more than two muons all possible f F~ combinations are plotted.

9 AN/ДМ Itvunts/ SO M«V) 3 m С 00 I 4 (evcnts/ioomtv) g S S S a AN/ДМ levenu/ioomfv) S S S 8-

10 AN/ДМ (events/100 MeV) о (Л о а. (О S 8

11 p and pf distributions for "background" events (.0 * M ( <t ^,9 GeV) and events with the mass of 3,1 GeV are presented in figs, 5 and 6, They appeared to be similar in shape. For example, both the "background" and 3/Ф events are exponentially dependent on p^ with the slopes 1.86 and,64 (GeV/c)", respectively(fig.6). If one subtracts the background in the mass range.9 f 3.3 GeV, then the slope will change by 0,07 (GeV/c)~. This value is to be compared with the statistical error equal to 0.3 (GeV/e). Thus the effect of background is negligible and when calculating the inclusive spectra, it was assumed that all the events with effective mass from.9 to 3.3 GeV resulted from 3/ф-*ц и The dependence of the spectrometer acceptance on p H decays. and p L was calculated by a Monte-Carlo method for three different assumptions on the angulsr distribution W (cos в., *? ) of mxons from f Z/ф -* ц + (Г in the rest frame of 3/Ф particle.- W = 1/4*, w = о = 3(1 + cos 0 }/1б!т, W = Ssin^ в /8n. In fig. 7 the histo- П i3 * grams present the measured cos 0^ and <f. distributions, smooth curves are expected angular dependences for three forms of W, obtained by Monte-Carlo calculations. Fig. 7 shows that calculated curves are close to each other and experimental data do not allow one to паке с preferable choice for any of W 4. However the shape of inclusive spectra for 3/Ф production turned out to be independent of type of W distributions. The choice for functions W determines the absolute value of the cross section. 10

12 ' / / P,,(GeV/c) Fig. 3. р щ diitribution of ii* u~ event» in two Baas region»:.0 r.9 GeV and.9 * f 3.3 GeV Ш 1.5 Fig:, в, p x distribution of /i /i~ events in two muss region»:.0 т.9 GeV and.9 т 3.3 GeV. Solid line represents the exponential fit to the'experimental data. Broken line reflects change in the elope when background Is subtra'-tod.

13 in о as o os 1 cos9 r f io 6 (rad) Fig. 7. Angular distribution for 3/Ф - n + e~ dec»y In the rest frame of J/Ц -p»rtlola, detected In the experiment (Matogrr*»). Saooth curves are expected distributions calculated by Monte-Carlo method for three forms of function W(see text)г J - W ~ ~sln a e rt, 3 - Wj» 1/4», 3 - W 3 -" I + cos 9 r f. The curves were calculated for p n rad p^ of /i + ц~ p«ir«obtained In experiment End.were normalized for the total number of event* In histogran. 1

14 In calculating inclusive spectra presented below isotropy for j/i/' ~> /i + fi~ decays was assumed. Dependence of geometric effi- ciency on p nnd p^ for this case is shown in fig. 8. do r d a J The dependence of inclusive cross section ~j up dx a dx dp on x = p* /p* " ax is presented in fig. 9, here t = p =1.5(GeV/c) imax and p* =5. (GeV/c). In the region x from 0.3 to 0.8 the inmax elusive spectrum falls exponentially with the slope CL=6.0±l..For x-to.3 the cross section deviates from this form and have become x independent within the statistical errors. Invariant cross sec- tion ~ / E* -^- dpf Cf ig. 10) and rapidity distribution dx о E* dxdp/ (fig. 11 and Table 1) exhibit similar behaviour. Equality of the cross sections Ла/Ду * f-0.1 < у * < 0} and Д ст/д у * (0 < y*< 0. 1) shows that the indicated flattening of inclusive spectra in the region of small p* is not caused by decrease of geometric efficiency of the spectrometer when p ^ 0 GeV/c ('see figs, 8 and 11). The values of the parameter Cl obtained in the experiments are enlisted in Table 1. Fig. 1 presents p distribution for J/Ф particle produo- L tion. The experimental data were fitted by the function -~ e dp *) It is assume, that j/ф particle is produced on nucleon at rest and (*) denotes the value in c.m. frame. 13

15 T a b l e 1 Incident Vaparticle P inc ri- + target able Range о form Parameter Ref. p + Be 30 p x 0<p x < 1.6 e"" bp i b = 1.6 /4/ p + Be 70 P 0<p <1.6 p 0 < p z < 1 0 x X e -bp _ Я т x 0.3<x<0.8 e a x У* 0.' -cy* e b = b = = с = This experiment p + Be 150 x C.l<x<0.7 e" -Qx a = 5 /5/ -~ + Fe 00 p 0.3< Pj< pf 0.1<pf<4 e-ax'.-a'x' a'= b'= b = a'= /6/ p + Fe 40 P l 0.3<p x < pf 0.1< Pl <4 b'=.+0.5 Ь = l.l±0.3 n + Be -50 x* x 1 > 0.5 p 0<pf<.5 e -av a'= Ю b = 1.5 /7/ (*) denotes the value in c.m. frame.. The momentum is in GeV/c, the slope b* is in (GeV/c) and the slope b is in (GeV/c)". 14

16 3 L APR. FEB. 10" \ ^V : \X \0 \ N50 \ \ 3 \ \го 3 i i i OS P?,(GeV/c) Fig. 8. Dependence of the «pectroaeter geonetric acceptance on р April run». and p x in February and 15

17 70 \ зо - \[ к \ )x 0 N \ \ N\ , Dependence of j/ф production cross section ~т ~ ** Г dp. on x D /v (t ^o о <!хф и в «х 'ли <Jx = 1.5 (GeV/c), p* = 5.г GeV/c). Pig. 10. x dependence of the invariant cross section for JA'' particle production. - (E * "^..x ^'(Cev/O?. P m " fix =5. GeV/c).

18 (Л (GeV/c)' Mg. 11. Dependence of J/<S production cross section on rapidity y*. W.g. 1. p^ dletrlbutlot-. for J/ii particle production.

19 For the interval 0 %p 4I.6 (GeV/c) th» slope b appeared to be equal to (GeV/c)" and it was (GeV/c)~ in the interval 0^ p i 1 (GeV/c). The values for the parameter b /4-7/ from ref. are given in Table 1. The data available allows one to make a conclusion that p^ distribution for J/ф production in nucleon-nuoleon interactions has the form of e~"pi. and the.slope b is constant in a wid.s energy range. 4. DIMOON PRODUCTION CROSS SECTIONS is given by The total cross section for the reaction p+be * (j/i/f*(i //")+. 1 1/4 A(p?)Ax _ a О ' -- \ Л.) N o e c 1- exp(-n a.) whore N o is the number of incident protons; 1 c is an efficiency of the detectors; <r a = 16 mbarns is the absorption cross section /8/ for protons on Be nuclei ; n is the number of nuclei per cm in the target; tj is the geometric acceptance for i-th event, summing over i was performed for the events in the region 0<:x 0.8 and 0<р (GeV/c). To obtain the cross section in the whole о range of kinematic variables one assumes that for x>0.8 and p > > 1.5 (GeV/c) differential cross section for J/ф production is proportional to exp(-6*-1.8p A ). Then the corresponding correo- 18

20 tions are equal to A(x) = and Л(Р А ) = 1.0? (factor takes into account the interval -7 < x< 0). The cross section calculated with formula (1) is equal to: a(p + Be-J/(i + ) = ( )-10~ 33 cm /nucleus. The error Includes both statistical and systematical ones. The values of obtained for isotropic decay of 3/ф-*р f were used In calculation. If the angular distribution of muons in the rest frame of 07V particles has the form 1 + cos в or sin 0, rf rf then the cross section should be tiultiplied by 1.3 or 0.73,respectively. The correction for background was 4%. The S/Ф production cross section in the first four units of the turget and four following ones turned out to be equal within statistical errors. Thus, j/ф production by secondaries is negligible. Using the value of F(j/V - >^r V-")/ ViJ/Ф * all) = one can obtain the total cross section for з/ф production; ст(р + Be^J/0+...) = ( )-10" 31 cm /nucleus. If the A - dependence of j/ф production Is о (nucleus) = /3 = a (nucleon) A, then 3 <r(p + N J/ ф + -P) = ( )' 10 cm /nucleon. The obtained cross section are about 5 times less than those measured at JWAL ^'. To make the comparison of the results from this and other experiments more convinieivt, the x dependence of the ratio c( x > 19

21 x ч!) fot J/^ particle production is presented in Table. Table X min <4 x o(-l«>*mln> x<ci) ing these cross sections it was assumed, that x and p Four events with M > 3.3 GeV (see figs.,3) we^-e detected in the experiment. They are all in the interval 3.4 * 3.7 GeV. The dependence of the production cross section per one ц* ~ event и in the region M > 3.5 GeV is shown in fig. 13. When calculates distributions of ц /л~ pairs are independent of M and have the forms, obtained for J/V, particles. The authors express their gratitude to A.A.Logunov, L.D.Soloviev, Yu.D.Prokoshkin, V.A.Yarba for interest and continuous support of this experiment, to S.S.Gershtein and A.K.Likhoded for useful discussions and ШЕР stuff who provided reliable operation of the accelerator and proton beam. We would like to thank CERN Administration for the permission to use a part of CER -IHEP Boson spectrometer equipment. 0

22 О» (nb) аз Л 5.5 IV (GeV) Fig. 13. Dependence of the /* + C~ production cross section per one event on effective mass Н да, When calculating "j It и assumed, that x and p? distributions for II + fi" pairs are Independent of U ufl and hive the forms as for J/i4 particles, 1

23 RJSFEREKCES, J.J.Aubert, U.Becker, P.J.Biggs et al. Phys. Rev. Lett., 33, 1404 (1974); J..E. Augustin, A.H.Boyarski, M.Breidenbach et al. Phys. Rev. Lett., 33, 1406 (1974). Yu.M.Antipov, V.A.Bessubov, N.I.Golovnya et al. Preprint IHEP 74-80, Serpukhov, (1974). Tu.M.Antipov, V.A.Bessubov, Ta.B.Busi.nin et al. Preprint IHEP 74-99, Serpukhov (1974). S.C.C.TiMg. A» Rapporteur's Summary at the International Conf. on High Energy Physics, Palermo, Italy, June 1975 and at the Intern. Symp. on Lepton and Photon Interactions at High Energies, Stanford University, August K.J.Anderson, G.G.Henry, K.T.McDonald et si. Paper presented at the Intern. Symp. on Lepton and Photon Interactions at High Energies, Stanford University, August G.J.Blanar, C.F.Boyer, W.L.Falssler et al. Preprint Northeastern University, Boston, June 1975; Paper presented at the - Intern. Symp. on Lepton and Photon Interactions at High Energies, Stanford University, August B.Knapp, W. Lee, P.Leung et al. Phys. Rev. Lett., 34, 1040 (1975); Paper presented at the Intern. Symp. on Lepton and Photon Interactions at High Energies, Stanford University, August S.P.Denisov, S.V.Dons4ov, Yu.P.Gorin et al. Preprint IHEP 73-, Serpukhov (1973); Tad. Fiz, 18, 336 (1973); Nuel. phys., B61. 6 (1973). Received 5 September 1975.

24 Пена 1 коп. - Институт физики высоких энергий, 1975, Издательская группа И Ф В Э Заказ 835. Тираж уч.-изд.л. Т Октябрь Редактор А.А. Антипова.