c

Volume 39B, number 2

GENERAL

PHYSICS LETTERS

CHARACTERISTICS IN N U C L E A R

OF

17 April 1972

PROTON-NUCLEON

EMULSION

AT

67

INTERACTIONS

GeV/c

M. G. ANTONOVA, E.G. BOOS, P.W. MOROZOVA, N.P. PAVLOVA, C.I. SHAKHOVA and Zh. S. TAKIBAEV High Energy Physics Institute of the Kazakh Academy of Sciences, Alma-Ata, USSR J. BABECKI, Z. CZACHOWSKA, B. FURMAI~SKA, R. HOLYI~SKI, K. KARNICKA, S. KRZYWDZINSKI, G. NOWAK and K. RYBICKI Institute of Nuclear Physics, Cracow, Poland

O. E. BADAWY*, N. P. BOGACHEV, N. DALKHAZHAV, R. KHOSHMUKHAMEDOV**, J. M. K O H L I ~ , G . S . SHABRATOVA and K. D. TOLSTOV Joint Institute for Nuclear Research, Dubna, USSR P. G. L E P E K H I N Physical-Technical Institute of the Soviet Academy of Sciences, Leningrad, USSR M. M. CHERNYAVSKY, N . B . MASLENNIKOVA, G. I. ORLOVA and M. I. TRETYAKOVA Physics Institute of the Soviet Academy of Sciences, Moscow, USSR

K. I. A L E K S E E V A Moscow State University, Moscow, USSR S. A. AZIMOV, A. Io BONDARENKO, L. P. CHERNOVA, G. M. CHERNOV, K.G. GULAMOV, U. G. GULYAMOV, V . V . LAVKOV, V. Sh. NAVOTNY, T . T . RISKIEV, N.S. SKRIPNIK, N. S. SVECHNIKOVA and T. P. TROFIMOVA Physical-Technical Institute of the Academy of Sciences of Uzbek SSR, Tashkent, USSR and

C. BATAAR, B. CHADRAA, G. SHARKIIUU, S. SUGAR and D. TUVDENDORZH Institute of Mathematics and Physics of the Mongolian Academy of Sciences, Ulan-Bator, Mongolia Received 21 February 1972 Interactions of 67 GeV/c protons with nucleons were studied in nuclear emulsion. Average proton-proton multiplicity is 6.63 • 0.16. Strong anisotropy of the angular distribution is seen. In this l e t t e r s o m e g e n e r a l c h a r a c t e r i s t i c s of p r o t o n - n u c l e o n i n t e r a c t i o n s at 67 G e V / c a r e r e ported . They w e r e studied by the c o l l a b o r a t i o n unde r the a u s p i c e s of the E m u l s i o n C o m m i t t e e of * On Leave of absence from Cairo University, UAR. ** On leave of absence from Physical-Technical Institute, Dushanbe, USSR. ~ O n leave of absence from the Punjab University, Chandigarh, India. 282

the Jo i n t Institute f o r N u c l e a r R e s e a r c h . P r e l i m i n a r y r e s u l t s w e r e p r e s e n t e d at the A m s t e r d am I n t e r n a t i o n a l C o n f e r e n c e on E l e m e n t a r y p a r t i c l e s [1]. C o h e r e n t i n t e r a c t i o n s of p r o t o n s a r e d e s c r i b e d in a n o t h e r p a p e r [2]. E x p e r i m e n t a l . An e m u l s i o n st ack 20 c m x 10 c m x 0.065 cm in s i z e was i r r a d i a t e d by (67±2) GeV/C p r o t o n s at the Serpukhov a c c e l e r a t o r . T h e adm i x t u r e of pions and kaons in the b e a m was l e s s

Volume 39B, number 2

PHYSICS LETTERS

than 1%. A l o n g - t h e - t r a c k s c a n n i n g for n u c l e a r i n e l a s t i c i n t e r a c t i o n s was p e r f o r m e d on the total length of 3057 m. The following type of events were not used for the c a l c u l a t i o n of the i n e l a s t i c - i n t e r action length Xint: i) s t a r s with single r e l a t i v i s t i c t r a c k s deflected by l e s s than 7 m r a d (mostly e l a s t i c s c a t ters), it) e l e c t r o n - p o s i t r o n p a i r s on the beam track, iii) knock-on e l e c t r o n s . Altogether 8239 i n e l a s t i c n u c l e a r i n t e r a c t i o n s were found, which c o r r e s p o n d s to ~int = (37.1 + 0.4) cm, the e r r o r being p u r e l y s t a t i s t i c a l . A c o m p a r i s o n of our r e s u l t with hint = (37.7 + 0.3) cm obtained p r e v i o u s l y [3] at (6 - 28) GeV/c shows that t h e r e is no g r e a t chaDge of the i n e l a s t i c p r o t o n - n u c l e o n c r o s s section up to 67 GeV/c. I n t e r a c t i o n s with f r e e and q u a s i - f r e e nucleons w e r e selected as those with at most one grey t r a c k (for a p r o t o n this c o r r e s p o n d s to kinetic energy between 25 MeV and 400 MeV) in the forward h e m i s p h e r e in the l a b o r a t o r y s y s t e m and without a v i s i b l e recoil nucleus. F o r e v e n - p r o n g n u m b e r (p-p) events t h e r e was the additional c r i t e r i o n of the a b s e n c e of an accompanying e l e c t r o n which could come f r o m the excitation of the t a r get nucleus. Altogether 1473 p r o t o n - n u c l e o n int e r a c t i o n s w e r e found, which r e p r e s e n t 18% of all i n e l a s t i c n u c l e a r i n t e r a c t i o n s in emulsion. F r o m its c o m p o s i t i o n one can e s t i m a t e that nearly half (~45%) of our 685 p-p stars correspond to collisions with free protons (i.e. emulsion hydrogen), the remain,trig ones being collisions with quasi-free protons of the emulsion nuclei. Odd-prong-number stars (p-n) correspond to collisions with quasi-free neutrons. As is estimated in the following p a p e r [2], t h e r e is a 25~o admixt u r e of c o h e r e n t i n t e r a c b o n s in our 788 odd-prong s t a r s . T h e r e f o r e in this l e t t e r we shall deal m a i n l y with p - p events which r e p r e s e n t a p u r e r s a m p l e of e l e m e n t a r y i n t e r a c t i o n s than p - n events. Prong number distribution. The p r o n g - n u m b e r n c h d i s t r i b u t i o n of p r o t o n - n u c l e o n events is shown in fig.1. An o v e r a b u n d a n c e o f n c h = 3 and nch = 1 s t a r s is i n t e r p r e t e d in t e r m s of coherent i n t e r a c t i o n s in a n o t h e r p a p e r [2]. The a v e r a g e m u l t i p l i c i t i e s for p - p and p - n i n t e r a c t i o n s a r e 6.63 + 0.16 and 6.17 + 0.22, r e s p e c t i v e l y . (Without c o r r e c t i o n for the c o h e r e n t events the l a t t e r m u l t i p l i c i t y is 5.42 + 0.16. ) The a v e r a g e m u l t i p l i c i t i e s for p - p c o l l i s i o n s at various total centre-of-massenergies ~CM are shown in fig.2. Our point at 67 GeV/c is slightly (by~ 0.3) above the power dependence
17 April 1972

d proton - neulron proton-proton coherent interactions

200

150

20~ n<~

Fig.l. Prong number distribution in proton-nucleon interactions at 67 GeV/c. The e r r o r s fOrnch = 1, 2, 3 and 5 include uncertainties connected with elastic and coherent events. The e r r o r s for the remaining multiplicities are purely statistical.

chamber data at lower energy [4]. The (nch} values obtained by the Echo Lake group [5] at cosmic-ray energies up to ~ 300 GeV are lower than our average multiplicity. We are aware th~ our r e s u l t can be affected by the influence of bound p r o t o n s . E.g. the r e a l t i v e l y thick tail of high m u l t i p l i c i t i e s nch L 10 in our work indicates that our e s t i m a t e of (nch) may be too l a r g e . Low energy e m u l s i o n data [6] on (nch) a r e 0.2 - 0.3 higher than the h y d r o g e n - b u b b l e - c h a m b e r ones at the s a m e energy, as can be seen in fig.2. On the other hand, any i n c r e a s e of the a v e r a g e multiplicity in i n t e r a c t i o n s with bound nucleons should be st r o n g e r in p - n events (only bound neutrons)

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Fig.2. Averagemuttiplicity~ch) versus totat centre-of mass energyE~t . 283

PHYSICS

Volume 39B, n u m b e r 2

-O

O

~'!

creasing multiplicity as was observed at lower energies. However, at our energy there is still a s i g n i f i c a n t a n i s o t r o p y up to rich = 12. T h e a u t h o r s a r e i n d e b t e d t o t h e w h o l e s t a f f of t h e I n s t i t u t e of H i g h E n e r g y a t S e r p u k h o v , i n p a r t i c u l a r to P r o f . Yu. D. P r o k o s h k i n a n d D r . S. D e n i sov, for their kind support and collaboration without which this experiment would not have been p o s s i b l e . T h e y a l s o e x p r e s s t h e i r t h a n k s to D r . S . I . L u b o m i l o v f r o m t h e J o i n t I n s t i t u t e for N u c l e a r R e s e a r c h f o r t h e f a s t p r o c e s s i n g of t h e e m u l s i o n . T h e g r e a t a m o u n t of w o r k d o n e b y o u r scanning teams is gratefully acknowledged.

II

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51 References

nt

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Fig.3. Angular distribution of secondary p a r t i c l e s in cos0 CM coordinate for various p-p multiplicities at 67 GeV/c. t h a n i n p - p e v e n t s (45% of h y d r o g e n ) , w h i l e t h e ~Zch)-Value in t h e f o r m e r i s s t i l l s m a l l e r t h a n in the latter. Angular distribution of secondary partwles. A n g u l a r d i s t r i b u t i o n s of s e c o n d a r y p a r t i c l e s f o r v a r i o u s p - p m u l t i p l i c i t i e s a r e s h o w n i n f i g . 3 , in c o s 0 C M - C O o r d i n a t e . T h e t r a n s f o r m a t i o n to t h e CMS w a s d o n e u s i n g t h e t r a n s v e r s e - m o m e n t u m distribution and other p-p data from lower energy r e s u l t s [7] s i m i l a r to w h a t w a s d o n e f o r p i o n s in r e f . [8]. A n a n i s o t r o p y of t h e a n g u l a r d i s t r t b u t i o n s is seen. This anisotropy decreases with the in-

284

17 April 19'~2

LETTERS

/

[1] Alma- Ata- Cracow-DUbna- L e n i n g r a d - M o s c o w - T a s h k e n t - U [ a n - B a t e r Collaboration, r e p o r t No. 263 at the A m s t e r d a m Intern. Conf. on E l e m e n t a r y p a r t i c l e s . [2] A l m a - A t a - Craeow-Dubna- L e n i n g r a d - M o s e o w - T a s h k e n t - l l l a n - B a t o r Collaboration, Phys. L e t t e r s 39B (1972) .285. [3] M e y e r , M.W. T e u c h e r and E. Lohrmann, Nuovo Cimento 28 (1963) 1299 (comisi[ation). [4] O. Czy~ewski and K. Rybieki, Institute of Nuclear Physics, r e p o r t No.703/PH, Cracow, 1970. [5] L.W. J o n e s et al., Phys. Rev. L e t t e r s 25 (1970) 1679. [6] The p-p multiplicities used here come f r o m the following h i g h - s t a t i s t i c s emulsion work: N. P. Bogachev, E . L . Grigoryev and Yu. P. Merekov, Dok[. Akad. Nauk SSR 148 (1963) 793; E. G. Boos, N. P. ]~avlova. T. T e m i r a v e v and R. A. Tursunov, Zh. E k s p e r i m . i. T e o r . Ffz. 47 (1964) 2041; S. A. Azimov, L. P. Chernova, G.M. Chernov and N. S. Svechnikova, Izv. Akad. Nauk SSSR 34 (1970) 1912. [7] R. R. Kinsey, T.W. M o r r i s and R. S. Panvini, BNL r e p o r t No. 1434, submitted to the Kiev Conference; D. B. Smith,. R . J . Sprafka and J. A. Anderson, Phys. Rev. L e t t e r s 23 (1969) 1064; E.W. Anderson et al., Phys. Rev. L e t t e r s 19 (1967)198. [8] B. Furmafiska, J. Gieruta, R. Holyfiski, S. Krzysdzifiski and A. Linscheid, Institute of Nuclear Physics, r e p o r t No. 761/PH.