- Email: [email protected]
Angular distribution of secondary particles produced in the intersecting storage rings at an energy equivalent to 1500 GeV
Volume 36B, n u m b e r 6
ANGULAR
PHYSICS
LETTERS
18 October 1971
DISTRIBUTION OF SECONDARY PARTICLES PRODUCED IN THE INTERSECTING STORAGE RINGS AT AN ENERGY EQUIVALENT TO 1500 GeV Bombay-CERN-Cracow
Collaboration*
Received 21 August 1971 The angular distribution of secondary r e l a t i v i s t i c charged p a r t i c l e s was m e a s u r e d in the ISR by means of nuclear emulsions used as detectors. The r e s u l t c o n f i r m s the c o s m i c - r a y observations of a dip in the angular distribution around 90 ° in the c e n t r e - o f - m a s s s y s t e m of the colliding protons.
T h e q u e s t i o n of t h e d i s t r i b u t i o n of l o n g i t u d i n a l m o m e n t a of s e c o n d a r y p a r t i c l e s p r o d u c e d in v e r y - h i g h - e n e r g y c o l l i s i o n s of h a d r o n s is of g e n e r a l i n t e r e s t , e s p e c i a l l y in c o n n e c t i o n w i t h t h e p r e d i c t i o n s m a d e by F e y n m a n a n d by Y a n g e t al. [1]. If t h e t r a n s v e r s e m o m e n t a c a n b e a s s u m e d i n d e p e n d e n t of t h e a n g l e a n d of t h e p r i m a r y e n e r g y , t h e d i s t r i b u t i o n of l o n g i t u d i n a l m o m e n t a o r , e v e n b e t t e r , t h a t of t h e l o n g i t u d i n a l r a p i d i t i e s i s r e p r o d u c e d in t h e a n g u l a r d i s t r i b u t i o n of s e c o n d a r y p a r t i c l e s in t h e c . m . s y s t e m of the colliding hadrons. This suggested a very s i m p l e e x p e r i m e n t at t h e C E R N I n t e r s e c t i n g Storage Rings. The intersection region was surr o u n d e d by n u c l e a r - e m u l s i o n p l a t e s a s d e t e c t o r s . T h e d e n s i t y of s e c o n d a r y r e l a t i v i s t i c c h a r g e d p a r t i c l e s w a s r e g i s t e r e d s i m u l t a n e o u s l y at v a r ious angles, giving the inclusive angular distribution integrated over all interaction channels, free from triggering biases. T h e f i r s t r e s u l t s of t h i s e x p e r i m e n t o b t a i n e d in i n t e r s e c t i o n I1 in a n e x p o s u r e p e r f o r m e d d u r i n g t h e n i g h t of 1 8 / 1 9 M a y 1971 w i t h 2 6 . 5 G e V p r o t o n s in b o t h b e a m s , a r e p r e s e n t e d h e r e . T h e c o l l i s i o n s a r e e q u i v a l e n t to c o l l i s i o n s of 1500-GeV protons with stationary target protons. Fig. 1 s h o w s t h e g e o m e t r y of t h e e x p e r i m e n t . T h e 6 0 0 - m i c r o n - t h i c k e m u l s i o n s on g l a s s ( I l f o r d G - 5 , 1 in. x 3 in.) w e r e m o u n t e d h o r i z o n t a l l y on a b a r in p o s i t i o n s at v a r i o u s a n g l e s c o v e r i n g t h e i n t e r v a l f r o m 90 ° t o 35 ° a s see,~ in fig. 1. T h e * Tata Institute of Fundamental R e s e a r c h , Bombay 5, India. CERN, NP Division, Emulsion Group, 1211 Geneva 23, Switzerland. Institute of Nuclear P h y s ics, Department V, Emulsion Group, Miekiewieza 30, Cracow, Poland.
a v e r a g e d i s t a n c e of t h e s e d e t e c t o r s f r o m t h e i n tersection "diamond" was about 2 m. The bar w i t h p l a t e s w a s p u t i n t o t h e f i n a l p o s i t i o n by m e a n s of a r e m o t e h a n d l i n g s y s t e m * * . T h i s w a s d o n e a f t e r t h e i n j e c t i o n a n d f i n a l p o s i t i o n i n g of b o t h b e a m s . T h e b a r w i t h e m u l s i o n s s t a y e d in t h i s p o s i t i o n f o r 9 h o u r s . T h e n it w a s r e m o v e d a g a i n b e h i n d t h e ISR s h i e l d i n g w e l l j u s t b e f o r e t h e b e a m s w e r e d u m p e d , in o r d e r not to e x p o s e t h e p l a t e s to s t r o n g r a d i a t i o n f r o m b e a m - p i p e interactions. T h e c u r r e n t of p r o t o n s in b o t h p i p e s w a s r e c o r d e d r e g u l a r l y d u r i n g t h e r u n . It w a s a b o u t 1A in e a c h p i p e . A l s o t h e b a c k g r o u n d r a d i a t i o n f r o m b o t h p i p e s w a s c h e c k e d by c o u n t e r t e l e s c o p e s , s h o w i n g no l a r g e f l u c t u a t i o n s ( f l a s h e s ) d u r i n g t h e 9 h o u r s of e x p o s u r e . T h e p l a t e s w e r e t h e n p r o c e s s e d a,ld s c a n n e d f o r f l a t m i n i m u m - i o n i z a t i o n tracks entering the plates from various direct i o n s . F i g . 2 s h o w s t h e a n g u l a r d i s t r i b u t i o n s of t h e s e t r a c k s o b s e r v e d in f o u r p o s i t i o n s of d e t e c t o r s : 90 ° , 70 ° , 50 ° a n d 35 ° ( c o r r e s p o n d i n g to 90 °, 67.1 °, 44.8 ° a n d 28.4 ° in t h e c . m . s y s t e m of the colliding protons). Each distribution shows a m a x i m u m in t h e r e g i o n w h i c h c o r r e s p o n d s to t h e d i r e c t i o n c o n n e c t i n g t h e p l a t e w i t h t h e c e n t r e of t h e i n t e r s e c t i o n of t h e p i p e s ( t h i s d i r e c t i o n i s c a l l e d 0 ° in fig. 2). T h e w i d t h of t h e b o t t o m of t h e s h a d e d a r e a s in fig. 2 c o r r e s p o n d s to t h e a n gular interval which the interaction "diamond" s u b t e n d s at t h e p o s i t i o n of t h e c o r r e s p o n d i n g e m u l s i o n d e t e c t o r . It c a n b e s e e n t h a t t h e m a x i m u m w i d t h of t h e p e a k s is in good a g r e e m e n t w i t h t h e s e p r e d i c t e d i n t e r v a l s (40 c m w a s a s ** We adapted for this purpose the "Telelift ~ s y s t e m supplied by Union-Kassenfabrik A.G.. ZUrich. 611
V o l u m e 36B, n u m b e r 6
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18 O c t o b e r 1971
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Fig. 1. G e n e r a l l a y - o u t of the e x p e r i m e n t in I1. T h e b l a c k r e c t a n g l e s i n d i c a t i n g the e m u l s i o n p l a t e s a r e not to s c a l e , in r e a l i t y t h e y h a v e ~ 2 t i m e s s m a l l e r d i m e n s i o n s . + and - indicate t h e s i g n s of a n g l e s u s e d in the s c a l e s in fig. 2. s u m e d a s t h e l e n g t h of t h e " d i a m o n d " ) . T h i s i n dicates that the tracks coming from other directions are due to the background of radiation prod u c e d in t h e w a l l s o f t h e p i p e s a n d in t h e m a g n e t ic s h i e l d i n g n e e d e d b y o t h e r e x p e r i m e n t s performed simultaneously in i n t e r s e c t i o n I1. T h e strongly directional radiation from pipe 1 is also clearly seen in the distributions corresponding t o d e t e c t o r s at 50 ° a n d 35 ° . W e s u b t r a c t e d t h i s b a c k g r o u n d s h o w n a s t h e d a s h e d l i n e s in f i g . ~.. We believe that the numbers of tracks corres p o n d i n g to t h e s h a d e d a r e a s a r e p r o d u c e d b y t h e secondaries emitted from the whole "diamond" 612
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Fig. 2. Raw a n g u l a r d i s t r i b u t i o n s of m i n i m u m - i o n i z a tion t r a c k s o b s e r v e d in n u c l e a r e m u l s i o n s at ISR l a b o r a t o r y a n g l e s i n d i c a t e d at the left s i d e of e a c h d i a g r a m . D a s h e d l i n e s a r e fitted to the b a c k g r o u n d . Shaded a r e a s c o r r e s p o n d to the r a d i a t i o n f r o m the " d i a m o n d " . T h e s c a n n e d e n t r a n c e a r e a of t h e d e t e c t o r at 35 ° is about two t i m e s s m a l l e r t h a n for e a c h of the o t h e r t h r e e d e tectors. in the directions of particular detectors. We normalized these numbers to the common solid angle and obtained in this way the relative intensities of charged relativistic secondaries at various angles*. Fig. 3 show these data indicating a * O u r definition of a r e l a t i v i s t i c p a r t i c l e is that its v e l o c i t y ~ 2,, 0.6. T a k i n g into a c c o u n t the l o s s e s in t h e wall of the b e a m tube and the m o t i o n of the c . o , m . r e f e r e n c e f r a m e , this m e a n s that the m o m e n t u m of the a c c e p t e d p i o n s e m i t t e d at 90 ° (see fig. I) is g r e a t e r than 100 MeV/c. T h i s cut r e j e c t s a f r a c t i o n of t r a c k s w h i c h is s m a l l in c o m p a r i s o n with o u r s t a t i s t i c a l e r r o r s , u n l e s s t h e r e is an a n o m a l y in t r a n s v e r s e m o m e n t a in the s e n s e that they a r e a n o m a l o u s ly s m a l l .
Volume36B, number 6
PHYSICS
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18 October 1971
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very strong anisotropy of the angular distribution. The da/dR drops by almost an order of magnitude between 90° and 35° in the ISR laboratory system. Fig. 4 shows the same data as function of l log tan ~Oc.m., compared with cosmic-ray results at about I000 GeV (fig. 4a) [2]. One observes a pronounced minimum in the angular distribution of secondaries in the neighbourhood of 90° in the c.m. system in agreement with many observations on cosmic-ray jets [3]. Several models (see e.g. the discussion by De Tar [4]) predict a flat distribution in longitudinal rapidity for the pions produced in very-high-energy proton-proton interactions. The variable log tan ½Oc.m. is, to a good approximation, linearly connected with the longitudinal rapidity [4]. As Lyon et al. have shown [5] the assumption of a flat distribution in rapidity leads to a corresponding distribution in log tan ½@c.m. which is a l m o s t f l a t but f a l l s off s l i g h t l y n e a r O c ' m " = 90 °. H o w e v e r , t h e v a l u e of d N / d { l o g t a n ½0 c ' m ' } at 90 ° is m o r e t h a n 80% of t h e p l a t e a u v a l u e e v e n f o r a p± c u t - o f f f u n c t i o n of t h e f o r m e x p ( - 1 5 p 2 ) . O u r d a t a a r e in d i s a g r e m e n t w i t h s u c h a p r e d i c tion. Fig. 4 b s h o w s o u r d a t a c o m p a r e d w i t h a s c a l i n g p r e d i c t i o n at 1500 G e V / c b a s e d on t h e d a t a of t h e S c a n d i n a v i a n C o l l a b o r a t i o n [6] f r o m 1 9 - G e V p p i n t e r a c t i o n s a n d c a l c u l a t e d by M i c h e j d a [7]. T h e d i f f e r e n c e b e t w e e n o u r d a t a and this prediction can be interpreted as an indicat i o n of a v i o l a t i o n of s c a l i n g f o r low v a l u e s of c . m , x = 2p :l / vrs in t h e e n e r g y r a n g e 1 9 - 1 5 0 0 G e V . In t h i s s e n s e t h e p r e s e n t e x p e r i m e n t i s c o m p l e m e n t a r y to t h e o n e d e a l i n g w i t h p a r t i c l e s
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Fig. 4. Differential relative c r o s s section do'/d {log tan 21-Oc.m.}. a) Ideogram shows the c o s m i c ray data at about 1000 GeV [2]. (b) Continuous line shows the scaling prediction according to Michejda [7]. e m i t t e d at a n g l e s b e t w e e n 5 ° and 17 ° w h e r e t h e x v a l u e s a r e l a r g e r t h a n a b o u t 0.08 [8]. W e a r e v e r y g r a t e f u l to P r o f e s s o r s B. P. G r e g o r y a n d W. J e n t s c h k e and to t h e s t a f f of t h e ISR D i v i s i o n f o r m a k i n g t h i s e x p e r i m e n t p o s s i b l e . We very much appreciate the help and hospitality e x t e n d e d t o u s by P r o f e s s o r H. S c h o p p e r , a n d we s h o u l d l i k e to t h a n k P r o f e s s o r G. C o c c o n i f o r discussions and his support. We are particularly i n d e b t e d to D r . H. BC~ggild f o r h i s h e l p in t h e i n t e r p r e t a t i o n of t h e d a t a . T h e i n s t a l l a t i o n of t h e e x p e r i m e n t w a s f a c i l i t a t e d g r e a t l y by t h e u n d e r s t a n d i n g c o o p e r a t i o n of M e s s r s . F. B o n a u d i a n d B. C o u c h m a n . M u c h of t h e m e c h a n i c a l e q u i p m e n t w a s p r e p a r e d in C r a c o w b y M e s s r s . W. K u b i c a , J. K n a p i k a n d W. J a n c z u r , a n d we s h o u l d l i k e t o thank them and the Cracow scanning team for t h e i r s k i l f u l w o r k . T h e h e l p of M e s s r s . U. B r o t s c h i , R. L o r e n z i a n d O. M e n d o l a at C E R N i s h i g h l y a p p r e c i a t e d . T h a n k s a r e d u e to D r . J . P e r n e g r f o r h i s v a l u a b l e c o m m e n t s on t h e m a n uscript.
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Volume 36B, n u m b e r 6
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References [1] R. P. F e y n m a n , Phys. Rev. L e t t e r s 23 (1969) 1415; J. Benecke, T. T. Chou, C.N. Yang and E. Yen, Phys. Rev. 188 (1969) 2159. [2] J. Gierula and W. Wolter, Acta P h y s i c a Polonica B2 (1971) 95. The i d e o g r a m in fig. 4a is the r e s u l t of the folding of the i d e o g r a m p r e s e n t e d in fig. 14 of this r e f e r e n c e . [3] P. Ciok, T. Coghen, J. Gierula, R. HotTnski, A. J u r a k , M. Micsowicz, T. Saniewska, O. Stanish and J. P e r n e g r , N u o v o C i m e n t o 8 (1958) 166; 10 (1958) 741; G. Cocconi, Phys. Rev. 111 (1958) 1699; J. Gierula, M. Miesowicz and P. Zielinski, Nuovo Cimento 18 (1960) 102;
614
[4] [5] [6] [7] [8]
18 October 1971
J. Gierula, D.M. Haskin and E. L o h r m a n n , Phys. Rev. 122 (1961) 626; F. A b r a h a m , J. Gierula, R. Levi Setti, K. Rybicki, C. H. Tsao, W. Wolter, R. L. F r i c k e n and R. W. Huggett, P r o c . Dubna Conf. on High e n e r g y p h y s i c s , 1964, p. 163; Phys. Rev. 159 (1967) 1110. C. De T a r , Phys. Rev. D3 (1971) 128. D. E. Lyon, C. Risk and D. Tow, Phys. Rev. 3D (1971) 104. H. B~ggild, K. H. J a n s e n and M. Suk, Nuel. Phys. B27 (1971) 1. L. Michejda, F u r t h e r t e s t of s c a l i n g p÷p--* ~'- + anything, paper p r e s e n t e d to the A m s t e r d a m Conf e r e n c e (1971). Nucl. P h y s . , to be published. L. G. Ratner, R . J . Ellis, G. Vannini, B . P . Babcock, A. D. K r i s c h and J. B. R o b e r t s , Phys. Rev. L e t t e r s 27 (1971) 68.
ANGULAR
PHYSICS
LETTERS
18 October 1971
DISTRIBUTION OF SECONDARY PARTICLES PRODUCED IN THE INTERSECTING STORAGE RINGS AT AN ENERGY EQUIVALENT TO 1500 GeV Bombay-CERN-Cracow
Collaboration*
Received 21 August 1971 The angular distribution of secondary r e l a t i v i s t i c charged p a r t i c l e s was m e a s u r e d in the ISR by means of nuclear emulsions used as detectors. The r e s u l t c o n f i r m s the c o s m i c - r a y observations of a dip in the angular distribution around 90 ° in the c e n t r e - o f - m a s s s y s t e m of the colliding protons.
T h e q u e s t i o n of t h e d i s t r i b u t i o n of l o n g i t u d i n a l m o m e n t a of s e c o n d a r y p a r t i c l e s p r o d u c e d in v e r y - h i g h - e n e r g y c o l l i s i o n s of h a d r o n s is of g e n e r a l i n t e r e s t , e s p e c i a l l y in c o n n e c t i o n w i t h t h e p r e d i c t i o n s m a d e by F e y n m a n a n d by Y a n g e t al. [1]. If t h e t r a n s v e r s e m o m e n t a c a n b e a s s u m e d i n d e p e n d e n t of t h e a n g l e a n d of t h e p r i m a r y e n e r g y , t h e d i s t r i b u t i o n of l o n g i t u d i n a l m o m e n t a o r , e v e n b e t t e r , t h a t of t h e l o n g i t u d i n a l r a p i d i t i e s i s r e p r o d u c e d in t h e a n g u l a r d i s t r i b u t i o n of s e c o n d a r y p a r t i c l e s in t h e c . m . s y s t e m of the colliding hadrons. This suggested a very s i m p l e e x p e r i m e n t at t h e C E R N I n t e r s e c t i n g Storage Rings. The intersection region was surr o u n d e d by n u c l e a r - e m u l s i o n p l a t e s a s d e t e c t o r s . T h e d e n s i t y of s e c o n d a r y r e l a t i v i s t i c c h a r g e d p a r t i c l e s w a s r e g i s t e r e d s i m u l t a n e o u s l y at v a r ious angles, giving the inclusive angular distribution integrated over all interaction channels, free from triggering biases. T h e f i r s t r e s u l t s of t h i s e x p e r i m e n t o b t a i n e d in i n t e r s e c t i o n I1 in a n e x p o s u r e p e r f o r m e d d u r i n g t h e n i g h t of 1 8 / 1 9 M a y 1971 w i t h 2 6 . 5 G e V p r o t o n s in b o t h b e a m s , a r e p r e s e n t e d h e r e . T h e c o l l i s i o n s a r e e q u i v a l e n t to c o l l i s i o n s of 1500-GeV protons with stationary target protons. Fig. 1 s h o w s t h e g e o m e t r y of t h e e x p e r i m e n t . T h e 6 0 0 - m i c r o n - t h i c k e m u l s i o n s on g l a s s ( I l f o r d G - 5 , 1 in. x 3 in.) w e r e m o u n t e d h o r i z o n t a l l y on a b a r in p o s i t i o n s at v a r i o u s a n g l e s c o v e r i n g t h e i n t e r v a l f r o m 90 ° t o 35 ° a s see,~ in fig. 1. T h e * Tata Institute of Fundamental R e s e a r c h , Bombay 5, India. CERN, NP Division, Emulsion Group, 1211 Geneva 23, Switzerland. Institute of Nuclear P h y s ics, Department V, Emulsion Group, Miekiewieza 30, Cracow, Poland.
a v e r a g e d i s t a n c e of t h e s e d e t e c t o r s f r o m t h e i n tersection "diamond" was about 2 m. The bar w i t h p l a t e s w a s p u t i n t o t h e f i n a l p o s i t i o n by m e a n s of a r e m o t e h a n d l i n g s y s t e m * * . T h i s w a s d o n e a f t e r t h e i n j e c t i o n a n d f i n a l p o s i t i o n i n g of b o t h b e a m s . T h e b a r w i t h e m u l s i o n s s t a y e d in t h i s p o s i t i o n f o r 9 h o u r s . T h e n it w a s r e m o v e d a g a i n b e h i n d t h e ISR s h i e l d i n g w e l l j u s t b e f o r e t h e b e a m s w e r e d u m p e d , in o r d e r not to e x p o s e t h e p l a t e s to s t r o n g r a d i a t i o n f r o m b e a m - p i p e interactions. T h e c u r r e n t of p r o t o n s in b o t h p i p e s w a s r e c o r d e d r e g u l a r l y d u r i n g t h e r u n . It w a s a b o u t 1A in e a c h p i p e . A l s o t h e b a c k g r o u n d r a d i a t i o n f r o m b o t h p i p e s w a s c h e c k e d by c o u n t e r t e l e s c o p e s , s h o w i n g no l a r g e f l u c t u a t i o n s ( f l a s h e s ) d u r i n g t h e 9 h o u r s of e x p o s u r e . T h e p l a t e s w e r e t h e n p r o c e s s e d a,ld s c a n n e d f o r f l a t m i n i m u m - i o n i z a t i o n tracks entering the plates from various direct i o n s . F i g . 2 s h o w s t h e a n g u l a r d i s t r i b u t i o n s of t h e s e t r a c k s o b s e r v e d in f o u r p o s i t i o n s of d e t e c t o r s : 90 ° , 70 ° , 50 ° a n d 35 ° ( c o r r e s p o n d i n g to 90 °, 67.1 °, 44.8 ° a n d 28.4 ° in t h e c . m . s y s t e m of the colliding protons). Each distribution shows a m a x i m u m in t h e r e g i o n w h i c h c o r r e s p o n d s to t h e d i r e c t i o n c o n n e c t i n g t h e p l a t e w i t h t h e c e n t r e of t h e i n t e r s e c t i o n of t h e p i p e s ( t h i s d i r e c t i o n i s c a l l e d 0 ° in fig. 2). T h e w i d t h of t h e b o t t o m of t h e s h a d e d a r e a s in fig. 2 c o r r e s p o n d s to t h e a n gular interval which the interaction "diamond" s u b t e n d s at t h e p o s i t i o n of t h e c o r r e s p o n d i n g e m u l s i o n d e t e c t o r . It c a n b e s e e n t h a t t h e m a x i m u m w i d t h of t h e p e a k s is in good a g r e e m e n t w i t h t h e s e p r e d i c t e d i n t e r v a l s (40 c m w a s a s ** We adapted for this purpose the "Telelift ~ s y s t e m supplied by Union-Kassenfabrik A.G.. ZUrich. 611
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18 O c t o b e r 1971
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Fig. 1. G e n e r a l l a y - o u t of the e x p e r i m e n t in I1. T h e b l a c k r e c t a n g l e s i n d i c a t i n g the e m u l s i o n p l a t e s a r e not to s c a l e , in r e a l i t y t h e y h a v e ~ 2 t i m e s s m a l l e r d i m e n s i o n s . + and - indicate t h e s i g n s of a n g l e s u s e d in the s c a l e s in fig. 2. s u m e d a s t h e l e n g t h of t h e " d i a m o n d " ) . T h i s i n dicates that the tracks coming from other directions are due to the background of radiation prod u c e d in t h e w a l l s o f t h e p i p e s a n d in t h e m a g n e t ic s h i e l d i n g n e e d e d b y o t h e r e x p e r i m e n t s performed simultaneously in i n t e r s e c t i o n I1. T h e strongly directional radiation from pipe 1 is also clearly seen in the distributions corresponding t o d e t e c t o r s at 50 ° a n d 35 ° . W e s u b t r a c t e d t h i s b a c k g r o u n d s h o w n a s t h e d a s h e d l i n e s in f i g . ~.. We believe that the numbers of tracks corres p o n d i n g to t h e s h a d e d a r e a s a r e p r o d u c e d b y t h e secondaries emitted from the whole "diamond" 612
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Fig. 2. Raw a n g u l a r d i s t r i b u t i o n s of m i n i m u m - i o n i z a tion t r a c k s o b s e r v e d in n u c l e a r e m u l s i o n s at ISR l a b o r a t o r y a n g l e s i n d i c a t e d at the left s i d e of e a c h d i a g r a m . D a s h e d l i n e s a r e fitted to the b a c k g r o u n d . Shaded a r e a s c o r r e s p o n d to the r a d i a t i o n f r o m the " d i a m o n d " . T h e s c a n n e d e n t r a n c e a r e a of t h e d e t e c t o r at 35 ° is about two t i m e s s m a l l e r t h a n for e a c h of the o t h e r t h r e e d e tectors. in the directions of particular detectors. We normalized these numbers to the common solid angle and obtained in this way the relative intensities of charged relativistic secondaries at various angles*. Fig. 3 show these data indicating a * O u r definition of a r e l a t i v i s t i c p a r t i c l e is that its v e l o c i t y ~ 2,, 0.6. T a k i n g into a c c o u n t the l o s s e s in t h e wall of the b e a m tube and the m o t i o n of the c . o , m . r e f e r e n c e f r a m e , this m e a n s that the m o m e n t u m of the a c c e p t e d p i o n s e m i t t e d at 90 ° (see fig. I) is g r e a t e r than 100 MeV/c. T h i s cut r e j e c t s a f r a c t i o n of t r a c k s w h i c h is s m a l l in c o m p a r i s o n with o u r s t a t i s t i c a l e r r o r s , u n l e s s t h e r e is an a n o m a l y in t r a n s v e r s e m o m e n t a in the s e n s e that they a r e a n o m a l o u s ly s m a l l .
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very strong anisotropy of the angular distribution. The da/dR drops by almost an order of magnitude between 90° and 35° in the ISR laboratory system. Fig. 4 shows the same data as function of l log tan ~Oc.m., compared with cosmic-ray results at about I000 GeV (fig. 4a) [2]. One observes a pronounced minimum in the angular distribution of secondaries in the neighbourhood of 90° in the c.m. system in agreement with many observations on cosmic-ray jets [3]. Several models (see e.g. the discussion by De Tar [4]) predict a flat distribution in longitudinal rapidity for the pions produced in very-high-energy proton-proton interactions. The variable log tan ½Oc.m. is, to a good approximation, linearly connected with the longitudinal rapidity [4]. As Lyon et al. have shown [5] the assumption of a flat distribution in rapidity leads to a corresponding distribution in log tan ½@c.m. which is a l m o s t f l a t but f a l l s off s l i g h t l y n e a r O c ' m " = 90 °. H o w e v e r , t h e v a l u e of d N / d { l o g t a n ½0 c ' m ' } at 90 ° is m o r e t h a n 80% of t h e p l a t e a u v a l u e e v e n f o r a p± c u t - o f f f u n c t i o n of t h e f o r m e x p ( - 1 5 p 2 ) . O u r d a t a a r e in d i s a g r e m e n t w i t h s u c h a p r e d i c tion. Fig. 4 b s h o w s o u r d a t a c o m p a r e d w i t h a s c a l i n g p r e d i c t i o n at 1500 G e V / c b a s e d on t h e d a t a of t h e S c a n d i n a v i a n C o l l a b o r a t i o n [6] f r o m 1 9 - G e V p p i n t e r a c t i o n s a n d c a l c u l a t e d by M i c h e j d a [7]. T h e d i f f e r e n c e b e t w e e n o u r d a t a and this prediction can be interpreted as an indicat i o n of a v i o l a t i o n of s c a l i n g f o r low v a l u e s of c . m , x = 2p :l / vrs in t h e e n e r g y r a n g e 1 9 - 1 5 0 0 G e V . In t h i s s e n s e t h e p r e s e n t e x p e r i m e n t i s c o m p l e m e n t a r y to t h e o n e d e a l i n g w i t h p a r t i c l e s
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Fig. 4. Differential relative c r o s s section do'/d {log tan 21-Oc.m.}. a) Ideogram shows the c o s m i c ray data at about 1000 GeV [2]. (b) Continuous line shows the scaling prediction according to Michejda [7]. e m i t t e d at a n g l e s b e t w e e n 5 ° and 17 ° w h e r e t h e x v a l u e s a r e l a r g e r t h a n a b o u t 0.08 [8]. W e a r e v e r y g r a t e f u l to P r o f e s s o r s B. P. G r e g o r y a n d W. J e n t s c h k e and to t h e s t a f f of t h e ISR D i v i s i o n f o r m a k i n g t h i s e x p e r i m e n t p o s s i b l e . We very much appreciate the help and hospitality e x t e n d e d t o u s by P r o f e s s o r H. S c h o p p e r , a n d we s h o u l d l i k e to t h a n k P r o f e s s o r G. C o c c o n i f o r discussions and his support. We are particularly i n d e b t e d to D r . H. BC~ggild f o r h i s h e l p in t h e i n t e r p r e t a t i o n of t h e d a t a . T h e i n s t a l l a t i o n of t h e e x p e r i m e n t w a s f a c i l i t a t e d g r e a t l y by t h e u n d e r s t a n d i n g c o o p e r a t i o n of M e s s r s . F. B o n a u d i a n d B. C o u c h m a n . M u c h of t h e m e c h a n i c a l e q u i p m e n t w a s p r e p a r e d in C r a c o w b y M e s s r s . W. K u b i c a , J. K n a p i k a n d W. J a n c z u r , a n d we s h o u l d l i k e t o thank them and the Cracow scanning team for t h e i r s k i l f u l w o r k . T h e h e l p of M e s s r s . U. B r o t s c h i , R. L o r e n z i a n d O. M e n d o l a at C E R N i s h i g h l y a p p r e c i a t e d . T h a n k s a r e d u e to D r . J . P e r n e g r f o r h i s v a l u a b l e c o m m e n t s on t h e m a n uscript.
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References [1] R. P. F e y n m a n , Phys. Rev. L e t t e r s 23 (1969) 1415; J. Benecke, T. T. Chou, C.N. Yang and E. Yen, Phys. Rev. 188 (1969) 2159. [2] J. Gierula and W. Wolter, Acta P h y s i c a Polonica B2 (1971) 95. The i d e o g r a m in fig. 4a is the r e s u l t of the folding of the i d e o g r a m p r e s e n t e d in fig. 14 of this r e f e r e n c e . [3] P. Ciok, T. Coghen, J. Gierula, R. HotTnski, A. J u r a k , M. Micsowicz, T. Saniewska, O. Stanish and J. P e r n e g r , N u o v o C i m e n t o 8 (1958) 166; 10 (1958) 741; G. Cocconi, Phys. Rev. 111 (1958) 1699; J. Gierula, M. Miesowicz and P. Zielinski, Nuovo Cimento 18 (1960) 102;
614
[4] [5] [6] [7] [8]
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J. Gierula, D.M. Haskin and E. L o h r m a n n , Phys. Rev. 122 (1961) 626; F. A b r a h a m , J. Gierula, R. Levi Setti, K. Rybicki, C. H. Tsao, W. Wolter, R. L. F r i c k e n and R. W. Huggett, P r o c . Dubna Conf. on High e n e r g y p h y s i c s , 1964, p. 163; Phys. Rev. 159 (1967) 1110. C. De T a r , Phys. Rev. D3 (1971) 128. D. E. Lyon, C. Risk and D. Tow, Phys. Rev. 3D (1971) 104. H. B~ggild, K. H. J a n s e n and M. Suk, Nuel. Phys. B27 (1971) 1. L. Michejda, F u r t h e r t e s t of s c a l i n g p÷p--* ~'- + anything, paper p r e s e n t e d to the A m s t e r d a m Conf e r e n c e (1971). Nucl. P h y s . , to be published. L. G. Ratner, R . J . Ellis, G. Vannini, B . P . Babcock, A. D. K r i s c h and J. B. R o b e r t s , Phys. Rev. L e t t e r s 27 (1971) 68.