c

Nuclear Physics BI21 (1977) 381--392 © North-Ilolland Publishing Company

SINGLE-PARTICLE INCLUSIVE SPECTRA OF CHARGED PARTICLES IN pp INTERACTIONS AT 22.4 GeV/e Alma-A ta-Dubna-Helsinki-Ko,~ice-Moscow-Prague Collaboration E.G. BOOS, V.V. SAMOJLOV, Zh. S. TAKIBAEV, M.A. TASHIMOV and T. TEMIRALIEV Institute of lligh Energy Physics, Ahna-Ata, USSR B.V. BATYUNYA, I.V. BOGUSLAVSKY, N.A. BUZDAVINA, I.M. GRAMENITSKY, V.G. IVANOV, R. LEDNICKY, L.A. TIKItONOVA, A. VALK,~ROV/~, V. VRBA and Z. ZLATANOV Joint Institute for Nuclear Research, Dubna, USSR J. ERVANNE, S. LJUNG, R. ORAVA, H. VILLANEN and P. VILLANEN Department of Nuclear Physics, University of Helsinki, ttelsinki, Finland J. PATOCKA institute of Experimental Physics, Ko]ice, CSSR B.V. KOROLEV, Ya. M. SELEKTOR, V.N. SHULYACHENKO and V.F. T U R O V Institute of Theoretical and Experimental Physics, Moscow, USSR R.K. DEMENTIEV, E.M. LEIKIN, A.G. PAVLOVA, N.A. POZHIDAEVA and V.I. RUD Institute for Nuclear Physics Research of the Moscow University, Moscow, USSR L. ROB and J. ZA~EK Faculty of Mathematics and Physics, Charles University, Prague, CSSR J. BOHM, J. CHELA, J. CVACH, I. HERYNEK, P. REIMER, J. SEDLAK and V. SIMAK Institute o f Physics, CSA V, Prague, CSSR Received 25 June 1976 (Revised 27 December 1976) The inclusive spectra for pp collisions at 22.4 GeV/c are investigated. We show that the transverse momentum distributions resemble those in h~h-energy pp interactions and discuss the influence of annihilation processes on the PT distributions. The invariant inclusive cross section for pions in the central region is found to be 28 ± I rob. A charge asymmetry is indicated by the y* spectrum in the central re,on, the asymmetry parameter having the value 0.15 ± 0.01. Finally, we estimate the upper limit of" the diffraction dissociation of the beam particle to bc 3.68 +0.45 -0.15 mb. 381

382

L: G. Boos et al. / Inclusive spectra o]" charged particles

1. Experimental procedure The experimental data presented in this paper were obtained from an exposure of the Serpukhov 2m hydrogen bubble chamber Ludmila to a 22.4 GeV/c RF separated antiproton beam. Tile technical details concerning tile experimental set-up, the beam characteristics and the scanning procedure are described in ref. [ 1 ]. Part of the pictures, corresponding to 0.217 -+ 0.002 events//ab, have been analyzed for this inclusive study. After measuring the events with semi-automatic devices we have processed them through the geomet,ical reconstruction programs Mass Dependent THRESH or HYDRA Geometry. Visual estimates of ionization were made of all tracks with momentum less than 1.5 GeV/c. For the events considered, no kinematical fitting of final state hypotheses is done, confronting us with tile following classes of charged secondaries: (a) momentum less than 1.5 GeV/c (protons and antiprotons identified by ionization), (b) momentum greater than 1.5 GeV/c. In kinematical calculations the secondary particles which were not labelled as protons or an antiprotons were taken as n-mesons. Inclusive spectra for positive pions are thus contaminated by a small fraction of protons and kaons. Kinematical distributions for negative particles are affected by K - mesons and fast antiprotons. The number of inelastic events with identified antiprotons is less than 1%, the rest of the negative tracks being labelled as pions. Our inelastic data sample consists of 7343 events. The elastic sample of I 175 events was selected applying a cut in the missing mass to the identified proton: Mx < 1.15 GeV and a simultaneous cut in the laboratory momentum of the negative secondary particle: Phb :> 19 GeV/c. Weights were calculated for each topology separately to account for scanning, measuring and processing losses, the average value being equal to 1.26. Losses caused by slow recoil protons in two prong events are estimated using the formula Ael = {OeI.Nto t - (Oto t • A i n ) N e l } / ( , ~ , / ' t o t

-- IVel } ,

(1)

where Ael and A i n stand for the losses of elastic and inelastic events, respectively. Nto t is the total weighted number of events and Nel the total weighted number of elastic events. The total and elastic cross sections, {~tot and oei, are taken from published results of counter experiments [2]. As the first approximation Ain was neglected and an estimate for the elastic losses was obtained: Act = 2.5 + 0.2 rob. The steep slope of der/dt and the small minimum value of the laboratory momentum of the recoiling proton for small M~ (Phb < 50 MeV/c f o r M 2 < 3 GeV 2) indicate, however, that the fraction of inelastic losses in this region is about the same as for elastic events. The estimate is A i n = 0.3 -+ 0.1 mb, the error including possible systematic shifts. Eq. (1) then gives Ael = 2.6 + 0.2 mb. Exponential parametrization of the four-momentum transfer distribution for the elastic events do/dt = A e x p ( - b t ) in the interval 0.06 ~< Itt ~< 0.30 (GeV/c) 2 (b = 12.0 -+ 0.6 (GcV/c) 2) leads to a loss consistent with the above estimate.

E: G. Boos et aL / hwlusive spectra o f charged particles

383

2. Momentum distributions

To illustrate the general behaviour of the charged secondaries we show in fig. 1 the lab momentum and in fig. 2 the transverse momentum squared distributions for positive secondary particles, negative secondaries and identified protons. Mainly diffractively produced, fast antiprotons are seen to peak at large momenta of the negative particle spectrum (fig. 1). The P?r distributions are well parametrized (table 1) by the exponential expression

do/dp 2 = (~ e x p ( - b , p ~ ) / I ,

(2)

+ (1 - o0 e x p ( - b 2 p ~ ) / l z ,

where I l and 12 are the normalization integrals of the type 1,, 2 = const. X f e x p ( - b , , a p ~ r)dp~r . The shapes of our p.~ distributions resemble those in the 100 GeV/c ~p experiment [3], our data lying slightly lower due to smaller charged particle multiplicities To allow comparison with pp data, we have plotted the p.~ distributions for pp experiments at 28.5 and 205 GeV/c [4,5] in fig. 2 as well. In table 2 we list the statistical parameters of the transverse momentum distributions obtained from our 22.4 GeV/c ~p data and from the 102 and 205 GeV/c pp data [5]. We note that the average PT values for charged secondaries in our experiment are close to the values obtained for negative pions produced in the reaction

21

22.4' GeV/C

171

,..... ~,p-negat.x

.&

~

02'

~,p-posLt..x

~'

L,

0

5

:": "" ~ '.:." ,.q..-", ,-!~:.."

10

15

R,,[c-,,vlc l

20

25

Fig. |. Lab. momentum distributions of secondary particles.

384

E.G. Boos et al. / Inclusive spectra o f charged particles

2f,

22.4 GoV]C ,.,._ #p- ne~at .x

~.

IC

rL #P-- POStt* x ~1~o~t- ~P-- Ptdent * X

~4 ~a

li

* (' iI

,

~4

02 !--i

02 04 Oe 08 W ~¢G,V/Oq

Fig. 2. Transverse momentum squared distributions. Tim solid line and the dash-dotted line show the distributions for the reaction pp -, n - + X at 205 [5J and 28.5 (;eV/c [4], respectively, the dashed line for the proton produced with - 1.0 ~ x ~ --0.5 in the reaction pp --, p + X at 205 GeV/c [5], the points for the reaction pp ~ n + + X at 100 GcV/c [3]. p p ~ 7r- + X at 102 a n d 205 G e V / c . O n e s h o u l d n o t e here t h a t the average PT a n d t h e dispersion D = [(p2> _ ( p x ) 2 ] 1/2 increase l o g a r i t h m i c a l l y w i t h e n e r g y for negative pions in the inclusivc processes: p p ~ 7r- + X, n + p -+ n - + X etc. up to 100 G e V / c [5] a n d e v e n t u a l l y r e a c h a p l a t e a u at a b o u t 2 0 0 G e V / c [6]. W h e n c o m p a r i n g t h e average PT values for d i f f e r e n t final s t a t e particles, we observe the f o l l o w i n g features: t h e ( p T ) for positive p i o n s p r o d u c e d w i t h an i d e n t i f i e d p r o t o n , = 284 -+ 2 M e V / c , o f the 12 G e V / c -p-p reactions [71. Next we m a k e an a t t e m p t to e s t i m a t e the average transverse m o m e n t u m in the a n n i h i l a t i o n c h a n n e l . S u p p o s i n g we can s e p a r a t e the average PT i n t o t w o c o m p o n e n t s c h a r a c t e r i s i n g t h e p r o d u c t i o n o f positive p i o n s in n o n - a n n i h i l a t i o n a n d anni-

"Fable l Mixing parameters and slopes obtained in the two-exponential fit of the p~- distributions Particle

p2[(GeV/c)2]

~

positive

0.04 - 1.0 0 . 0 4 - 1.0 0.0 - 1.0 0.0 1.0

0.45 0.24 0.51 0.48

P

~r+ negative

± 0.04 ± 0.10 ± 0.03 ± 0.03

b I [(GeV/c) -2 ]

b2[(GeV/c) - 2 ]

×2/NDF

13.1 ± 0.8 17.1 ± 5.0 15.2 ± 0.7 15.3 ± 0.7

3.9 5.6 4.1 4.0

57.5/44 39.6/44 70.2/46 45.3/46

± 0.2 ± 0.4 ± 0.2 ± 0.1

1£G. Boos et al. / Inclusive spectra of charged particles

385

Table 2 Statistical parameters of the transverse momentum distributions (Errors are only statistical) Reaction Momentum [(,eV/c] .

.

.

.

.

.

.

pp

.

.

.

.

.

.

.

.

.

.

22.4

102 205

PP

(p2) [(;eV/c) 2 ]

D = ((p2).. (pT)2)l/2 [GeV/c]

positive 0.344 _+0.003 negative 0.354 ± 0.003 n+ 0.342 - 0.003 p 0.357 +- 0.005

0.170±0.003 0.188 ± 0.003 0.171 ± 0.003 0.164 t 0.004

0.227±0.003 0.250 ± 0.003 0.232 ± 0.003 0.191 ± 0.005

nn-

0.170±0.010 0.166 +- 0.003

0.228±0.010 0.220 ± 0.004

Particle .

.

.

.

.

.

(pT) [GeV/c ] .

.

.

.

0.343 -+ 0.010 0.343 ± 0.004

h i l a t i o n c h a n n e l s , we write t h e following r e l a t i o n (PT) = a(PT )NA + (1 - a) (p.l-) A ,

(3)

w h e r e a is the f r a c t i o n o f positive pions in the n o n - a m l i h i l a t i o n chatmels. E x t r a p o lating the e x i s t i n g a n n i h i l a t i o n cross section data frotn lower energies we get OA = 8.5 + 0.5 m b at 2 2 . 4 G e V / c . Our events w i t h an i d e n t i f i e d p r o t o n t h e n c o m p o s e a c o n s i d e r a b l e f r a c t i o n o f a b o u t 40% o f the n o n - a n n i h i l a t i o n events. A s s u m i n g n o w t h a t the lab m o m e n t u m spectruxn (fig. 1) for the identified p r o t o n s does not fall o f f slower t h a n that for all positive secondaries, we are able to e s t i m a t e the relative a m o u n t o f i d e n t i f i e d p r o t o n s f r o m all inelastically p r o d u c e d p r o t o n s to be a b o u t 75%. We t h e n c o n s i d e r t h e value (PT) for the n+'s in events w i t h an identified prot o n as a good a p p r o x i m a t i o n for t h e average transverse m o m e n t u m o f t h e charged pions p r o d u c e d in n o n - a n n i h i l a t i o n c h a n n e l s (possible isospin d e p e n d e n c e o f (pT)NA in the NN collisions at o u r energy is here neglected). C o n s i d e r i n g the n o n - a n n i h i l a t i o n topological probabilities to be the same as in events w i t h an identified p r o t o n (see table 3), we get for the f r a c t i o n a = 0.55 +- 0.03, a n d t a k i n g the probabilities from pp data at 24 G e V / c [8] we get the result a = 0.65 Fable 3 Inelastic cross sections in millibarns Prongs

°P-Ptopa)

otPgp(24 GeV/c) b)

oi~9.proto n

2 4 6 8 10 12

8.81 14.17 9.45 4.25 1.42 0.24

8.70 12.55 6.71 2.17 0.40 0.04

3.26 5.32 2.11 0.40 0.07 0.01

± 0.90 ± 0.32 ± 0.24 ± 0.15 ± 0.08 ± 0.03

a) Ref. [ll, b) Ref. 181.

± 0.25 ± 0.10 ± 0.07 ± 0.04 ± 0.02 ± 0.01

± 0.35 ± 0.19 ±0.11 ± 0.05 ± 0.02 ± 0.01

386

~: G. Boos et aL /Inclusive spectra of charged particles

"!-0.02. The average multiplicities fl)r positively charged pions in the annihilation and non-annihilation channels, corresponding to the fractions above, then are: (n) A = 4.2 -+ 0.4, (n) NA = 1.9 +- 0.1 and (n) A = 3.3 +- 0.3, (/I}NA = 2.12 -+ 0.02, respectively. Taking the uncertainty between the two values of fractions a into account relation (3) gives us (pT)A = 420 +- 30 MeV/c, the value standing two standard deviations higher than the result (pT)A = 361 +- 2 MeV/c obtained at 12 GeV/c [7]. The contribution of the steeper exponent in parametrization of eq. (2) (o~ = 0.51 + 0.03) is close to the earlier fraction a, indicating that the flatter exponential behaviour o f the p-I- distribution could be due to the annihilation processes. In fact, the flatter exponent yields for the average transverse momentum (Pr) = 438 + 12 MeV/c, close to the value (pT)A obtained before. One shot, ld note further, that the p-I- spectrum for the negatively charged particles in our data at high transverse momentum has less steep behaviour than in the pp data at 28.5 GeV/c (fig. 2) again indicating that annihilation mainly contributes to the flatter exponential.

3. Single-particle distributions In fig. 3 we plot the cenue-ol:mass rapidity distributions for positively and negalively charged pions including the 14.75 and 100 GeV/c ~p data [9, 31 for comparison. The invariant inclusive cross section at ),* ~ 0 is 28 + 1 mb. We have rel]ected the rr+ rapidity distribution abot, t y * = 0, which thus gives us the corresponding rr- spectrum because of CP conservation. The difference between the distributions o f the reflected n +'s and the negative particles in the forward direction is caused by the unidentified amiprotons. The inclusive cross section in the central region is seen to be approximately constant in the energy interval from 15 to 100 (;eV/c. Next we plot the invariant cross section

1 /-2/."*

d2o

for charged pions m fig. 4 with the data from the reactions zr-p -+ 7r- + X at 100 GeV/c [10] and pp ~ rr- + X at 28.5 and 102 GeV/c [4,5]. The distribution for positively charged pions is reflected about x = 0 and shown only in the forward direction, which enables comparison with the reaction pp --* zr- + X also m this re, o n (for the backward direction the x-distribution, not shown, ahnost coincides with the spectrum of the negative pions). Our distribution for n - ' s is seen to be closer to thal of the pp reactions at 102 GeV/c m the backward henrisphere than in the forward hcmisphere, whcrc our rclqected rr+ spectrum is significantly broader than the 102 GeV/c rr- spectrum.

l:" G. Boos et aL / Inclusive spectra o f charged particles

387

22.4 GeV/C

~ , p - ne~at ,. x

:..

pp-n'.x

•

z,O

• ~ v• . a"*{ ,., 20 tt

~.j

. . . .

i {,-,, :.":

"t v

4 ,.o

rJ

:

'..f

~

1

'1

i

o4

02 o.1

-3

-2

-I

0

y"

1

2

3

Fig. 3. The rapidity distributions in the centre-of-mass system. The points show the distribution for the reaction ~p .--, 7r+ + X at 100 (,eV/c [3], the squarcs for the reaction ~p ~ n - + X at 14.75 GcV/c [9]. The distributions for n + mesons are rellectcd abouty* = 0.

The n o r m a l i z e d invariant cross sections (1/O~o t ( d o / d ) , ) at Ylab = 0, i.e. in the target f r a g m e n t a t i o n region, for re- p r o d u c t i o n in various r e a c t i o n s are given in fig. 5 as f u n c t i o n s o f s - 1 / 2 . A rapid decrease o f the f r a g m e n t a t i o n cross s e c t i o n for the p r o d u c t i o n process ~ p ~ n - + X in the P ~ b interval f r o m 4.5 to 22.4 G e V / c fits the p r e d i c t i o n o f l l u m b l e [11 ] (solid line). The p r e d i c t i o n is based o n the multiperipheral m o d e l w i t h t h e a s s u m p t i o n s o f high multiplicities a n d s t r o n g energy dep e n d e n c e in the a n n i h i l a t i o n processes. The d i s t r i b u t i o n (1/Oin) ( d a / d x ) , s h o w n in fig. 6 *, for negatively charged pions has larger values in the f o r w a r d h e m i s p h e r e t h a n in the b a c k w a r d onc, p a r t i c u l a r l y at small lxl, c o r r e s p o n d i n g to the shift o f the m a x i m u m in t h e y * d i s t r i b u t i o n . To investigate this effect f u r t h e r , we use e x p o n e n t i a l p a r a m e t r i z a t i o n d o / d x = A exp(-b± Ixl) for the f o r w a r d (b+) a n d b a c k w a r d ( b _ ) h e m i s p h e r e s separately in different intervals Ixl ~ 1.5 GeV/c increases the corresponding x-value. The shift is inverscb proportional to tile laboratory nlomentunl of the secondary particle: ,~x ~ (0.44 (;eV/c)/Pla b. For the values x ~ 1 tile effect ix negligible but becomes sibmificant for x ~ 0.2 as indicated by tile excess of positive particles over negative ones in the region o f x ~ 0 and the opposite effect for 0.2 ~ x ~< 0.6, which can be seen in the figure.

/z; G. Boos et al. I Inclusive spectra of charged particles

388

22.4 GoV/C ~p-- ne~lat + × iL. P P ~ / 7 % X

:',. 10

..~ r~

¢'~1I £k

i

¢~b-~

,

i~,

..L~.,

e J~ , }

of

- ! i.

,..J

'l

L,

I

e~l,,O ><

r"

~:

IX~

U

,: # Ii1 i! "'-~

011 . '. !

7

I

~: ?

"1

t L..;

I

L,.: II

.......

-06-0.4-02

~1 I

;

I

I..~.

I

:

i

0

02 0.,~ 06 08 x . P~ Prna~

~0

Fig. 4. lnvariant cross section distributions

/(x)

= ±f2E__, °in

d2o

.'~/s ~ d p ~ . d P T '

The solid line shows the distribution for the reaction n - p ---*rr- + X at 100 GcV/c [ 10], the dashed line and the squares for the reaction pp ~ rr- ÷ X at 28.5 and 102 (,eV/c [4,5], respectively. The distribution for rr+ mesons is rellcctcd about x :: 0, and shown only in the forward direction. and b _ = 10.0-+ 0.2 giving for the ratio o f the slopes R =

b_/b÷ =

1.61 -+ 0.02 a

value close to the result R ~ 1.5 obtained in meson-nucleon interactions I121, whereas f i o m a simple free quark m o d e l one expects R = 1 for antinucleon-nucleon zmd R = 1.5 for meson-nucleon interactions. For the interval Ixl ~< 0.16 we get a smaller value t\~r R, R = 1.33 -+ 0.07, which is due to the decrease o f the contribution o f the backward hemisphere when broadening the x-interval. For x 0 = 0.16 the a s y m m e t r y para,neter B = (Nf - N h ) / ( N f + Nh), where N f ( N b ) is the n u m b e r o f particles going forward (backward) in the centre-of-mass, has the value B = 0.15 -+ 0.01. The a s y m m e t r y o f the x-distribution and the shift o f the m a x i m u m in the y * distribution can be explained in a multiperip.heral model by a beam (target) chargc trans. fer into the central region [13]. We remark furlher, that it has been shown that this a s y m m e t r y increases with the transverse m o n i e n t u m [14 I. The a s y m m e t r y parameter B in the interval b'*t < 1 equals 0.07 +- 0.01 for PT < 0.5 G e V / c and 0.25 -+ 0.05 for PT > 1.0 GoV/c. Such a p h e n o n i c n o n is present also in 7r-p reactions at 205 G c V / c [1 5], and is explaincd by the parton model [ 16] but not by the multiperiphe-

E. (;.

Boos et

389

al. /Inch~sive spectra o f charged particles

e..{o.vlcI 0.30

241612 8 6

ISR

PP-*IT- ] , * n~'P''"H-~ EXOTIC"

o r'P-*rl" J

025

• n-P-n-~.

~ 0.26

x

i NOn*

Pp--IT-

/

---HuEL LER/REGGE/

--HUMSLE

]

/

~

0.15

0

011

0.2

0.3

s'~,lGov"] Fig. 5. Target fragmentation cross sections (1/O~o~) ( d o / d y ) v = 0 (Otot = 39.8 m b [6]) for different inclusive reactions as functions of s - 1 / 2 .

10

22.4 GeV/C

:: PP-negat" X n_ PP-- POSd..x

I

0.1 -05

0

05

1D

,

x.P_2._ •

.

.

Fig. 6. x-distributions of secondary particles. The distributions tor the p o s n w e and the n ticles arc reflected about x = O.

-t-

par-

390

E G. Boos et aL /Inclusive spectra o]charged particles

6°°ll '-1

,

20O 4001

024 6 810

20

,o

2o

,o

- ~0

20

~"

20

30

30

200t __ (C)

1 ,oot

"°°I ,b o 2oo]

~-.=¢,0011 [~a) E

0 2 4 6 8"t0

MflG,'v'l

Fig. 7. Missing mass squared distributions to the identified proton (a) for 2-prong events. (b) for 4-prong events, (c) for > 6-prong events, and (d) for all topologies.

ral model. One should note that a simple quark fusion model is also used to explain the large PT phenomena in pp collisions [17]. The ISR results have been recently interpreted in a valence quark model [I 8] assuming the donlinance o f tile quarkdiquark scattering amplitude. These models suggest an explanation at least for the high PT part of the observed forward-backward asymmetry in ~p collisions.

4. Antiproton diffraction dissociation Evidence for target and beam particle diffractive dissociation has been found in a number of experiments. For example, in the reaction pp -~. p + X there is an enhancement at low missing mass values (Mx2 < 5 GeV 2) corresponding to tile diffraction dissociation o f the incident proton. The cross section for this cnhanccment depends weakly on energy, and the differential cross section do/dt is similar to that of elastic scattering [5]. We show in fig. 7 the missing mass squared distribulions to the identified proton for different topologies of our events. For two-prong events there is a pronounced peak at about Mx2 ~ 2 GeV 2. For four-prong events only some shoulder in this region is seen and for higher topolo~es the low-nlass region remains ahnost unpopulated. In table 4 we compare the cross sections for the low-mass enhancement, defined by the cut M2/s < 0.16, in the production processes ~p --* p + X at 22.4 and 32.1 GeV/c [I 9]. The cross sections are found to be the same within two standard deviations, our value lying, however, systematically higher.

E. G. Boos et al. / Inclusive spectra of charged particles

391

Table 4 Upper limits for the beam fragmentation cross sections in mb for the reaction pp ~ p + X with M~/s < 0.16 Prongs

22.4 GeV/c

32.1 GeV/c .

2

0.41 a) 2.25 ± 0.11

1.8 ± 0.2

4

1.31 -+0.09

1.I ± 0.2

0.12 ± 0.02 0.45 a) 3.68 t 0.15

2.9 ± 0.3

>/6 all

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a) The error includes inelastic losses.

We note further, that the reflected x-distribution in fig. 6 for positively charged particles resembles the one for negative particles in the region x -~ 1. This indicates that target and beam particle dissociation cross sections are of the same order of magnitude as it should follow from the CP symmetry of the ~p interactions.

5. Conclusions We summarize the main results of this an',dysis as follows: (i) The transverse momentum distributions show similar features as those of pp collisions at incident momenta higher than 100 GeV/c. An indication is foulld that the average transverse momentum in annihilation channels is larger than in nonannihilation reactions. (ii) The centre of mass rapidity distribution for pions resembles the spectrum at 14.75 GeV/c incident momentum and coincides with the 100 GeV/c spectrum at 3,* -~ 0 as well. (iii) Charge asymmetry is found in the central region. The asymmetry parameter has the value 0.15 -+ 0.01 in the interval 0 ~< [xl ~< 0.16. (iv) The upper limit of tile antiproton diffraction dissociation cross section is +o.4ss rob. The corresponding value at 32.1 GeV/c is 2.9 -+ 0.3 rob. found to be 3.68 -o.]

The authors want to express their gratitude to the staff responsible for the operation of the Serpukhov accelerator and of the beana channel no. 9 and to the technical staff of the Ludmila HBC. We also thank the technicians and assistants at all laboratories for their excellent work. The authors flora the Moscow State University want to express their gratitude to Professor V.G. Shevchenko for his continuous support of this work.

392

k: G. Boos et al. / lnchtsive spectra o f charged particles

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