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Observation of cascade hyperon interactions
Volume
38B,
number
2
PHYSICS
OBSERVATION
OF
CASCADE
LETTERS
HYPERON
24 January
INTERACTIONS
1972
*
R. A. M U L L E R
Space Sciences Laboratory and Lawrence Berkeley Laboratory, University of California, Berkeley, Calif. 94720, USA Received 28 December 1971
We r e p o r t on the observation of 17 --o + P interactions in the Berkeley 72" Hydrogen Bubble Chember. C r o s s - s e c t i o n s are calculated for both elastic and inelastic channels.
A l t h o u g h the e x i s t e n c e of the c a s c a d e h y p e r o n (~ p a r t i c l e ) h a s b e e n known s i n c e 1953, t h e r e h a v e b e e n v i r t u a l l y no r e p o r t s of i t s i n t e r a c t i o n s . T h e r e h a v e b e e n m a n y s t u d i e s of the i n t e r a c t i o n s of o t h e r s t r a n g e h y p e r o n s ; the n e g l e c t of the ~p a r t i c l e c o m e s not f r o m l a c k of i n t e r e s t but r a t h e r f r o m l a c k of p a r t i c l e s . B e c a u s e of i t s low p r o d u c t i o n c r o s s - s e c t i o n , the t o t a l l e n g t h of t r a c k s p r o d u c e d in h y d r o g e n b u b b l e c h a m b e r s , f o r e x a m p l e , i s p r o b a b l y l e s s t h a n 1000 m e t e r s . We t h o u g h t t h a t it m i g h t be i n t e r e s t i n g to look a t the i n t e r a c t i o n s of s u c h s t r a n g e p a r t i c l e s . We m a d e a s e a r c h f o r ~ r e a c t i o n s in f i l m t a k e n in an e x p o s u r e of the B e r k e l e y 72" b u b b l e c h a m b e r to K - p a r t i c l e s in 1963. The p r o d u c t i o n and d e c a y c h a r a c t e r i s t i c s of t h e ~ ' s f r o m t h i s e x p o s u r e h a v e b e e n r e p o r t e d p r e v i o u s l y [1]. D u r i n g the i n i t i a l p h a s e s of t h i s w o r k , the f i r s t p u b l i s h e d c r o s s - s e c t i o n s f o r e l a s t i c ~--+ p s c a t t e r i n g w a s r e p o r t e d by C h a r l t o n et al. [2] and by the A m s t e r d a m - N i j m e g e n C o l l a b o r a t i o n [3]. We r e p o r t h e r e the o b s e r v a t i o n of 4 E - + p and 13~ ° + p i n t e r a c t i o n s . T h i r t e e n of t h e s e i n t e r a c t i o n s w e r e in i n e l a s t i c c h a n n e l s . T h e m o m e n t a of the ~ ' s r a n g e d f r o m a low of 0.5 G e V / c to a h i g h of 2.8 G e V / c . T h e a v e r a g e m o m e n t u m of the E ' s in the c h a m b e r w a s 1.3 G e V / c ; t h e a v e r a g e m o m e n t u m of t h e ~ ' s w h i c h i n t e r a c t e d w a s 2.0 G e V / c . T h e h i g h e r a v e r a g e m o m e n t u m of the i n t e r a c t i n g s a m p l e i n d i c a t e s a c r o s s - s e c t i o n w h i c h r i s e s with e n e r g y . i n t e r a c t i o n t o p o l o g i e s w e r e too r a r e to h a v e b e e n i n c l u d e d a s an e v e n t t y p e in the o r i g i nal s c a n n i n g of the f i l m , d o n e s o o n a f t e r the 1963 e x p o s u r e . H o w e v e r t h e r e w a s a s p e c i a l * Work supported in part by the Atomic Energy Commission, and in part by the National Aeronautics and Space Administration.
category for peculiar events (traditionally called " z o o - o n s " ) , and it w a s into t h i s c a t e g o r y t h a t m o s t of the ~ i n t e r a c t i o n s s h o u l d h a v e b e e n c l a s s i f i e d . We m a d e a s p e c i a l s c a n of s e v e r a l t h o u s a n d z o o - o n s , an~l found 32 c a n d i d a t e s f o r i n t e r a c t i o n s . Of the 17 w h i c h w e e v e n t u a l l y c a l l e d t r u e ~ i n t e r a c t i o n s , a l l but two had b e e n t a g g e d a s z o o - o n s on both s c a n s . T h u s the o v e r a l l s c a n n i n g e f f i c i e n c y w a s c l o s e e n o u g h to 100% that scanning bias e r r o r s w e r e negligible c o m p a r e d to o u r s t a t i s t i c a l e r r o r s . T h e r e w e r e not e n o u g h e v e n t s to p e r m i t a t o p o l o g y - d e p e n d e n t c a l c u l a t i o n of s c a n n i n g e f f i c i e n c y . All c a n d i d a t e s w e r e m e a s u r e d at l e a s t t h r e e t i m e s , k i n e m a t i c a l l y fit with the p r o g r a m SIOUX, and r e - s c a n n e d f o r c o n s i s t e n c y with p r e d i c t e d i o n i z a t i o n . P a r t i c u l a r c a r e w a s t a k e n to t r y n o n h y p o t h e s i s on t h o s e e v e n t s that had a good fit to a ~ i n t e r a c t i o n h y p o t h e s i s . K i n e m a t i c f i t s w e r e a c c e p t e d if t h e y had a c o n f i d e n c e l e v e l of 1% o r b e t t e r . T h e r e s u l t s of o u r s e a r c h a r e s u m m a r i z e d in t a b l e 1. In o r d e r to be s u r e that an e v e n t r e p r e s e n t e d a ~ i n t e r a c t i o n , we r e q u i r e d (depending on the e v e n t type) (a) that a K + o r v i s i b l e K ° w a s p r o d u c e d a l o n g with the ~ , a n d / o r (b) that a v i s i b l e A w a s s e e n in the f i n a l s t a t e . The c o l u m n marked "signature" indicates which conditions w e r e p l a c e d on e a c h e v e n t t y p e . F o r the d e t e r m i n a t i o n of i n t e r a c t i o n c r o s s - s e c t i o n s we c o u l d u s e o n l y t h o s e e v e n t s f o r w h i c h we k n e w the t o t a l p a t h l e n g t h of ~ ' s in o u r e x p o s u r e . T h u s , f o r e x a m p l e , w e c o u l d not u s e ~ ° ' s t h a t w e r e p r o d u c e d in the p a r t i c u l a r r e a c t i o n K- + p ~o ~ o + K o+ To (even if the ~ i n t e r a c t e d and the K ° d e c a y e d ) , b e c a u s e we did not k n o w the r a t e at w h i c h ~ ° ' s a r e p r o d u c e d in t h i s r e a c t i o n . The n u m b e r of e v e n t s f o r e a c h r e a c t i o n t y p e that c o u l d b e u s e d f o r the c r o s s - s e c t i o n d e t e r m i n a t i o n J23
Volume 38B, number 2
PHYSICS
24 January 1972
LETTERS Table i
reaction
cross-section events **
events *
signature
~O+p~--.O+p
2
K,A
1
8
~ O + p ~ A+ E+
6
A
4
24
~o + p.__~EO+E+
1
A
1
6
~ ° + p ~ 7r++A+A =O+p__ ~O+A+X+
1 1
K,A A
1
6
1
6
~O+p~?T++~-+p
1
K or A
1
5
~ O + p ~ ~'++~'+ +~-+ n
i
K,A
1
6
.--o+p~ ~ - +p
2
A
2
8
~O+p~ E-+E+
1
K
1
4
~O+p__E-+KO+p
1
K
1
4
c r o s s - s e c t i o n (mb)
* Confidence level from SIOUX >/ 1 ~. ** Includes only those events for which a ~ pathlength could be calculated.
is listed in the next column of the table. Pathlength of the ='s was determined for each signature type, using the data of ref. [1]. C r o s s - s e c tions for each reaction (corrected for unseen events) are listed in the last column. In all cases the e r r o r s are determined by statistics; scanning losses and other systematic e r r o r s are negligible. Rather than specify an e r r o r for each reaction cross-section, we simply give the number of events used in its computation. Our e l a s t i c - o +p interaction cross-sections are compatible with those published previously [2, 3]. Inelastic cross-sectionshave never been published before. It is interesting to note that i n t e r a c t i n g ~ - ° ' s a r e r e l a t i v e l y e a s y to i d e n t i f y , e v e n though E ° ' s t h a t d e c a y ( b e c a u s e they d e c a y i n t o n e u t r a l s ) a r e d i f f i c u l t to i d e n t i f y . F o r the - O + p i n t e r a c t i o n o u r total observed c r o s s - s e c t i o n i s 61 + 20 rob; the t o t a l c r o s s - s e c t i o n s h o u l d include c o n t r i b u t i o n s f r o m such final s t a t e s as E ° + p + ~ °. no ~+ Only in o n e r e a c t i o n , -~ + p ~ A + = , were t h e r e s u f f i c i e n t e v e n t s to w a r r a n t l o o k i n g at the a n g u l a r d i s t r i b u t i o n . F o r t h i s r e a c t i o n , the c e n t e r of m a s s a n g u l a r d i s t r i b u t i o n w a s c o n s i s t e n t w i t h a flat d i s t r i b u t i o n : the c o s i n e s of the
124
a n g l e b e t w e e n the i n c o m i n g - o and t h e o u t g o i n g A w e r e - 0 . 6 9 , - 0 . 4 5 , -0.05, 0.05, 0.15, and 0.80 f o r the s i x e v e n t s . The t o t a l o b s e r v e d c r o s s s e c t i o n s f o r ~ O + p is of the s a m e o r d e r a s o t h e r b a r y o n - b a r y o n c r o s s - s e c t i o n s ; at t h i s s t a g e of i n v e s t i g a t i o n t h e r e s e e m s to be n o t h i n g p e c u l i a r a b o u t -~ i n t e r a c t i o n s . P e t e r Cook d e s e r v e s s p e c i a l m e n t i o n f o r h i s e x c e l l e n t c o m p u t e r p r o g r a m m i n g and c a r e f u l s c a n n i n g , and f o r h i s i n i t i a t i v e in t h e s e i n v e s t i g a t i o n s . I w i s h a l s o to t h a n k L u i s A l v a r e z f o r s u g g e s t i n g and e n c o u r a g i n g t h i s w o r k .
References [1] P.M. Dauber, J. P. Berge, J . R . Hubbard, D.W. M e r r i l l and R. A. Muller, Phys. Rev. 179 (1969) 1262. [2] G. R. Charlton, J. Badier, E. B a r r e l e t , I. Makarovisch, J. P e r n e g r , J . R . Hubbard, A. Leveque C. Louedec, L. Moscoso and D. Revel, Phys. Letters 32B (1970) 720. [3] R. R. Dalmeijer, A.J. de Groot, J. C. Kluyver, E. de L i j s e r and H . J . G . Tiecke, Lettere al Nuovo Cimento 4 (1970) 373.
38B,
number
2
PHYSICS
OBSERVATION
OF
CASCADE
LETTERS
HYPERON
24 January
INTERACTIONS
1972
*
R. A. M U L L E R
Space Sciences Laboratory and Lawrence Berkeley Laboratory, University of California, Berkeley, Calif. 94720, USA Received 28 December 1971
We r e p o r t on the observation of 17 --o + P interactions in the Berkeley 72" Hydrogen Bubble Chember. C r o s s - s e c t i o n s are calculated for both elastic and inelastic channels.
A l t h o u g h the e x i s t e n c e of the c a s c a d e h y p e r o n (~ p a r t i c l e ) h a s b e e n known s i n c e 1953, t h e r e h a v e b e e n v i r t u a l l y no r e p o r t s of i t s i n t e r a c t i o n s . T h e r e h a v e b e e n m a n y s t u d i e s of the i n t e r a c t i o n s of o t h e r s t r a n g e h y p e r o n s ; the n e g l e c t of the ~p a r t i c l e c o m e s not f r o m l a c k of i n t e r e s t but r a t h e r f r o m l a c k of p a r t i c l e s . B e c a u s e of i t s low p r o d u c t i o n c r o s s - s e c t i o n , the t o t a l l e n g t h of t r a c k s p r o d u c e d in h y d r o g e n b u b b l e c h a m b e r s , f o r e x a m p l e , i s p r o b a b l y l e s s t h a n 1000 m e t e r s . We t h o u g h t t h a t it m i g h t be i n t e r e s t i n g to look a t the i n t e r a c t i o n s of s u c h s t r a n g e p a r t i c l e s . We m a d e a s e a r c h f o r ~ r e a c t i o n s in f i l m t a k e n in an e x p o s u r e of the B e r k e l e y 72" b u b b l e c h a m b e r to K - p a r t i c l e s in 1963. The p r o d u c t i o n and d e c a y c h a r a c t e r i s t i c s of t h e ~ ' s f r o m t h i s e x p o s u r e h a v e b e e n r e p o r t e d p r e v i o u s l y [1]. D u r i n g the i n i t i a l p h a s e s of t h i s w o r k , the f i r s t p u b l i s h e d c r o s s - s e c t i o n s f o r e l a s t i c ~--+ p s c a t t e r i n g w a s r e p o r t e d by C h a r l t o n et al. [2] and by the A m s t e r d a m - N i j m e g e n C o l l a b o r a t i o n [3]. We r e p o r t h e r e the o b s e r v a t i o n of 4 E - + p and 13~ ° + p i n t e r a c t i o n s . T h i r t e e n of t h e s e i n t e r a c t i o n s w e r e in i n e l a s t i c c h a n n e l s . T h e m o m e n t a of the ~ ' s r a n g e d f r o m a low of 0.5 G e V / c to a h i g h of 2.8 G e V / c . T h e a v e r a g e m o m e n t u m of the E ' s in the c h a m b e r w a s 1.3 G e V / c ; t h e a v e r a g e m o m e n t u m of t h e ~ ' s w h i c h i n t e r a c t e d w a s 2.0 G e V / c . T h e h i g h e r a v e r a g e m o m e n t u m of the i n t e r a c t i n g s a m p l e i n d i c a t e s a c r o s s - s e c t i o n w h i c h r i s e s with e n e r g y . i n t e r a c t i o n t o p o l o g i e s w e r e too r a r e to h a v e b e e n i n c l u d e d a s an e v e n t t y p e in the o r i g i nal s c a n n i n g of the f i l m , d o n e s o o n a f t e r the 1963 e x p o s u r e . H o w e v e r t h e r e w a s a s p e c i a l * Work supported in part by the Atomic Energy Commission, and in part by the National Aeronautics and Space Administration.
category for peculiar events (traditionally called " z o o - o n s " ) , and it w a s into t h i s c a t e g o r y t h a t m o s t of the ~ i n t e r a c t i o n s s h o u l d h a v e b e e n c l a s s i f i e d . We m a d e a s p e c i a l s c a n of s e v e r a l t h o u s a n d z o o - o n s , an~l found 32 c a n d i d a t e s f o r i n t e r a c t i o n s . Of the 17 w h i c h w e e v e n t u a l l y c a l l e d t r u e ~ i n t e r a c t i o n s , a l l but two had b e e n t a g g e d a s z o o - o n s on both s c a n s . T h u s the o v e r a l l s c a n n i n g e f f i c i e n c y w a s c l o s e e n o u g h to 100% that scanning bias e r r o r s w e r e negligible c o m p a r e d to o u r s t a t i s t i c a l e r r o r s . T h e r e w e r e not e n o u g h e v e n t s to p e r m i t a t o p o l o g y - d e p e n d e n t c a l c u l a t i o n of s c a n n i n g e f f i c i e n c y . All c a n d i d a t e s w e r e m e a s u r e d at l e a s t t h r e e t i m e s , k i n e m a t i c a l l y fit with the p r o g r a m SIOUX, and r e - s c a n n e d f o r c o n s i s t e n c y with p r e d i c t e d i o n i z a t i o n . P a r t i c u l a r c a r e w a s t a k e n to t r y n o n h y p o t h e s i s on t h o s e e v e n t s that had a good fit to a ~ i n t e r a c t i o n h y p o t h e s i s . K i n e m a t i c f i t s w e r e a c c e p t e d if t h e y had a c o n f i d e n c e l e v e l of 1% o r b e t t e r . T h e r e s u l t s of o u r s e a r c h a r e s u m m a r i z e d in t a b l e 1. In o r d e r to be s u r e that an e v e n t r e p r e s e n t e d a ~ i n t e r a c t i o n , we r e q u i r e d (depending on the e v e n t type) (a) that a K + o r v i s i b l e K ° w a s p r o d u c e d a l o n g with the ~ , a n d / o r (b) that a v i s i b l e A w a s s e e n in the f i n a l s t a t e . The c o l u m n marked "signature" indicates which conditions w e r e p l a c e d on e a c h e v e n t t y p e . F o r the d e t e r m i n a t i o n of i n t e r a c t i o n c r o s s - s e c t i o n s we c o u l d u s e o n l y t h o s e e v e n t s f o r w h i c h we k n e w the t o t a l p a t h l e n g t h of ~ ' s in o u r e x p o s u r e . T h u s , f o r e x a m p l e , w e c o u l d not u s e ~ ° ' s t h a t w e r e p r o d u c e d in the p a r t i c u l a r r e a c t i o n K- + p ~o ~ o + K o+ To (even if the ~ i n t e r a c t e d and the K ° d e c a y e d ) , b e c a u s e we did not k n o w the r a t e at w h i c h ~ ° ' s a r e p r o d u c e d in t h i s r e a c t i o n . The n u m b e r of e v e n t s f o r e a c h r e a c t i o n t y p e that c o u l d b e u s e d f o r the c r o s s - s e c t i o n d e t e r m i n a t i o n J23
Volume 38B, number 2
PHYSICS
24 January 1972
LETTERS Table i
reaction
cross-section events **
events *
signature
~O+p~--.O+p
2
K,A
1
8
~ O + p ~ A+ E+
6
A
4
24
~o + p.__~EO+E+
1
A
1
6
~ ° + p ~ 7r++A+A =O+p__ ~O+A+X+
1 1
K,A A
1
6
1
6
~O+p~?T++~-+p
1
K or A
1
5
~ O + p ~ ~'++~'+ +~-+ n
i
K,A
1
6
.--o+p~ ~ - +p
2
A
2
8
~O+p~ E-+E+
1
K
1
4
~O+p__E-+KO+p
1
K
1
4
c r o s s - s e c t i o n (mb)
* Confidence level from SIOUX >/ 1 ~. ** Includes only those events for which a ~ pathlength could be calculated.
is listed in the next column of the table. Pathlength of the ='s was determined for each signature type, using the data of ref. [1]. C r o s s - s e c tions for each reaction (corrected for unseen events) are listed in the last column. In all cases the e r r o r s are determined by statistics; scanning losses and other systematic e r r o r s are negligible. Rather than specify an e r r o r for each reaction cross-section, we simply give the number of events used in its computation. Our e l a s t i c - o +p interaction cross-sections are compatible with those published previously [2, 3]. Inelastic cross-sectionshave never been published before. It is interesting to note that i n t e r a c t i n g ~ - ° ' s a r e r e l a t i v e l y e a s y to i d e n t i f y , e v e n though E ° ' s t h a t d e c a y ( b e c a u s e they d e c a y i n t o n e u t r a l s ) a r e d i f f i c u l t to i d e n t i f y . F o r the - O + p i n t e r a c t i o n o u r total observed c r o s s - s e c t i o n i s 61 + 20 rob; the t o t a l c r o s s - s e c t i o n s h o u l d include c o n t r i b u t i o n s f r o m such final s t a t e s as E ° + p + ~ °. no ~+ Only in o n e r e a c t i o n , -~ + p ~ A + = , were t h e r e s u f f i c i e n t e v e n t s to w a r r a n t l o o k i n g at the a n g u l a r d i s t r i b u t i o n . F o r t h i s r e a c t i o n , the c e n t e r of m a s s a n g u l a r d i s t r i b u t i o n w a s c o n s i s t e n t w i t h a flat d i s t r i b u t i o n : the c o s i n e s of the
124
a n g l e b e t w e e n the i n c o m i n g - o and t h e o u t g o i n g A w e r e - 0 . 6 9 , - 0 . 4 5 , -0.05, 0.05, 0.15, and 0.80 f o r the s i x e v e n t s . The t o t a l o b s e r v e d c r o s s s e c t i o n s f o r ~ O + p is of the s a m e o r d e r a s o t h e r b a r y o n - b a r y o n c r o s s - s e c t i o n s ; at t h i s s t a g e of i n v e s t i g a t i o n t h e r e s e e m s to be n o t h i n g p e c u l i a r a b o u t -~ i n t e r a c t i o n s . P e t e r Cook d e s e r v e s s p e c i a l m e n t i o n f o r h i s e x c e l l e n t c o m p u t e r p r o g r a m m i n g and c a r e f u l s c a n n i n g , and f o r h i s i n i t i a t i v e in t h e s e i n v e s t i g a t i o n s . I w i s h a l s o to t h a n k L u i s A l v a r e z f o r s u g g e s t i n g and e n c o u r a g i n g t h i s w o r k .
References [1] P.M. Dauber, J. P. Berge, J . R . Hubbard, D.W. M e r r i l l and R. A. Muller, Phys. Rev. 179 (1969) 1262. [2] G. R. Charlton, J. Badier, E. B a r r e l e t , I. Makarovisch, J. P e r n e g r , J . R . Hubbard, A. Leveque C. Louedec, L. Moscoso and D. Revel, Phys. Letters 32B (1970) 720. [3] R. R. Dalmeijer, A.J. de Groot, J. C. Kluyver, E. de L i j s e r and H . J . G . Tiecke, Lettere al Nuovo Cimento 4 (1970) 373.