DSpace at VNU: OBSERVATION OF CORRELATIONS BETWEEN VECTOR-MESON AND BARYON-RESONANCE DECAYS

Volume 18, number PHYSICS LETTERS C.De Vries, R.Hofstadter, A.Johansson and R Herman, Phys Rev 134 (1964) B 848 10 P.Stein, R.W.McAllister, B.D.McDaniel and W M Woodward, Phys Rev Letters (1962) 403; P Stein, M Binkley, R~ W McAllister, B.D McDaniel and W M Woodward, Proc Intern Conf at Stanford University (1963) p 373 1August1965 11 B.Grossetete, preprint L.A.L.Orsay, to be published 12 J.R.Dunning J r , K.W.Chen A.A.Cone, G.Hartwig, N F Ramsey, J.K Walker and R Wilson, Phys.Rev.Letters 13 (1964) 631 13 F.M.Renard, J.Tr~n Thanh V~n and M.Le Bellac, Orsay TH 86 (to be published) ***** OBSERVATION OF CORRELATIONS AND BARYON-RESONANCE BETWEEN VECTOR-MESON DECAYS * G GOLDHABER, J L BROWN, I BUTTERWORTH, S GOLDHABER, A.A HIRATA, J A KADYK, B C SHEN and G H TRILLING Depart~nent of Physics and Lawrence Radiation Labo~'atory, University of California, Berkeley, California Received 24 June 1965 In our s t u d i e s of d o u b l e - r e s o n a n c e f o r m a t i o n in the channel M + + p - V ° + ~M++- A ++ Lp+~ +' (i) we have "observed marked angular correlations between the decay angular distribution of the vector meson and that of the ~, ~ baryon resonance A++(1238) Here M + represents the ~+ or K + meson and V ° the pO or K ~° vector-meson resonance respectively As is well known [1-5], for s m a l l v a l u e s of f o u r - m o m e n t u m t r a n s f e r squared, t the decay a n g u l a r d i s t r i b u t i o n s at the two v e r t i c e s for these r e a c t i o n s follow the g e n e r a l f e a t u r e s of a p s e u d o s c a l a r m e s o n exchange model However, the a c t u a l d i f f e r e n t i a l production c r o s s s e c t i o n s d i s a g r e e s t r o n g l y with s i m p l e exchange m o d e l s Two r e m e d i e s for this difficulty with the p s e u d o s c a l a r m e s o n exchange model have been suggested One has been the i n t r o d u c t i o n of f o r m f a c t o r s at the r e s p e c tive v e r t i c e s [6] The a l t e r n a t i v e has b e e n to c o n s i d e r a b s o r p t i o n effects due to i n i t i a l - and f i n a l - s t a t e i n t e r a c t i o n s [7, 8] The a u g u l a r - c o r r e l a t i o n effects we have o b s e r v e d i n d i c a t e that f i n a l - s t a t e i n t e r a c t i o n s play a n i m p o r t a n t r o l e and t h e r e f o r e i m p l y the need to conSider a b s o r p tion effects In this note we p r e s e n t e x p e r i m e n t a l data * Work done under the auspices of the U S Atomic Energy Commission 76 showing the e x i s t e n c e of decay c o r r e l a t i o n s between the K *° and the A ++ resonances~ v e r y s i m l i a r to those o b s e r v e d between the po and A++ r e s o n a n c e s [1, 2] T h e s e data come f r o m three d i s t i n c t e x p e r i m e n t s , all c a r r i e d out in the Brook haven National L a b o r a t o r y ' s - i n c h bubble chamb e r exposed in the B r o o k h a v e n - Y a l e s e p a r a t e d b e a m [9] at the A.G.S The e x p e r i m e n t s involve the following r e a c t i o n s : ~+p , ~+~'~+p at 3.65 GeV/c [10] (2) K+p * K+~-~+p at 1.96 GeV/c [11] (3) K+d * K+~-~+p(n) at 2.3 GeV/c (4) In r e a c t i o n (4) the K+p channel was s e p a r a t e d f r o m the K+n c h a n n e l by demanding that the labor a t o r y m o m e n t u m of the n e u t r o n be l e s s than that of the proton, and f u r t h e r , l e s s than 300 MeV/c With these c r i t e r i a , the m o m e n t u m d i s t r i b u t i o n for the n e u t r o n a g r e e s well with that given by the Hulth~n wave function for the deuteron, and its l a b o r a t o r y a n g u l a r d i s t r i b u t i o n is a p p r o x i m a t e l y i s o t r o p i c , showing that it is r e a s o n a b l e to t r e a t it as a s p e c t a t o r to a r e a c t i o n on the proton as target It has been shown e a r l i e r that a p p r e c i a b l e f r a c t i o n s of r e a c t i o n s (2) and (3) p r o c e e d v i a d o u b l e - r e s o n a n c e f o r m a t i o n [10, 11] We note h e r e that r e a c t i o n (4) is also dominated by K *° and A++ p r o d u c t i o n and that a s i g n i f i c a n t p r o p o r tion of the r e a c t i o n goes via t h e i r s i m u l t a n e o u s p r o d u c t i o n in a q u a s i - t w o - b o d y p r o c e s s This may be s e e n f r o m fig 1, which shows the phase- Volume 18, number PHYSICS LETTERS s p a c e t r i a n g l e plot of % + v e r s u s MK+~ f o r the data at 2.3 G e V / c The n u m b e r of e v e n t s i n v o l v e d in the t h r e e e x p e r i m e n t s a r e 1784, 410 and 904, r e s p e c t i v e l y Of t h e s e , the n u m b e r s a s s i g n e d to V °A ++ "double r e s o n a n c e " f o r m a t i o n a r e 555, 262 and 426, and finally, the n u m b e r s of e v e n t s which fulfill o u r s m a l l - f o u r - m o m e n t u m - t r a n s f e r cutoff c r i t e r i o n , t < 0.5 GeV 2, a r e 429, 124 and 248 r e s p e c t i v e l y ~ T h e s e l a s t t h r e e n u m b e r s c o r r e s p o n d to the s a m ple with which we a r e c o n c e r n e d h e r e We have c o m p a r e d the data in r e a c t i o n s (3) and (4) on K$°A ++ p r o d u c t i o n and find t h e m s u f f i c i e n t ly s i m i l a r to p e r m i t t h e i r c o m b i n a t i o n f o r g r e a t e r s t a t i s t i c a l a c c u r a c y In what f o l lo w s we u s e the c o m b i n e d data f o r t h e s e r e a c t i o n s To study the a n g u l a r c o r r e l a t i o n e f f e c t we show S c a t t e r p l o t s of cos ~ A v e r s u s c o s ~V w h e r e t h e s e r e p r e s e n t the a n g l e s b e t w e e n the " i n c i d e n t " p r o t o n and s c a t t e r e d p r o t o n in the A++ c e n t r e of m a s s s y s t e m and the i n c i d e n t and outgoing M + in the V° c e n t r e of m a s s s y s t e m r e s p e c t i v e l y (see figs 2a and 3a) To obtain a q u a n t i t a t i v e m e a s u r e of the o b s e r v e d c o r r e l a t i o n s , we have p l o t te d the d e c a y a n g u l a r d i s t r i b u t i o n of the V ° m e s o n f o r t h r e e i n t e r v a l s in cos ~A T h e s e a r e the two p o l a r i n t e r v a l s cos ~A = - to - and +0.4 to + 1.0 and the e q u a t o r i a l i n t e r v a l - to +0.4 C o n v e r s e l y cos ~A has a l s o been p lo tt e d f o r the s a m e t h r e e i n t e r v a l s of c o s ~V" T h e s e d i s t r i b u tions a r e shown in figs b - g and 3b-g The c u r v e s shown in t h e s e f i g u r e s r e p r e s e n t the b e s t f i t to the e x p a n s i o n [(cos ~) = A + B co s ~ + C cos2ot The c o e f f i c i e n t s n o r m a l i z e d to A = 1.0 a r e l i s t e d in t a b l e s and The f i t s a r e good, and h i g h e r - o r d e r t e r m s a r e not r e q u i r e d F o r a p u r e p s e u d o s c a l a r m e s o n exchange no an g u l ar i n f o r m a t i o n can be t r a n s m i t t e d between v e r t i c e s , and hence one e x p e c t s no c o r r e l a t i o n to o c c u r Thus e a c h of the t h r e e d i s t r i b u t i o n s in cos ~V and cos o~A would have to be identical As m a y be r e a d i l y noted by e x a m i n i n g figs and 3, two d i s t i n c t d i f f e r e n c e s in the t h r e e d i s t r i b u tions f o r cos ~A a r e : (a) The d i s t r i b u t i o n s in cos ~A c o r r e s p o n d i n g to the two p o l ar r e g i o n s of co s ~V show a m a r k e d d i f f e r e n c e The d i s t r i b u t i o n in cos ~A which g o e s with cos ~V in the i n t e r v a l 0.4 to 1.0, i.e., c o r K + d -~ K + T r - T r + p I /r /r 1130 MeV~< Mp#+ ~< 1300 MeV, 840 MeV ~