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THE IMPORTANCE OF POLARIZATION IN KAON PHOTOPRODUCTION AND RADIATIVE CAPTURE
S. Cotanch, R. Williams, Chueng-Ryong Ji
To cite this version:
S. Cotanch, R. Williams, Chueng-Ryong Ji. THE IMPORTANCE OF POLARIZATION IN KAON
PHOTOPRODUCTION AND RADIATIVE CAPTURE. Journal de Physique Colloques, 1990, 51
(C6), pp.C6-491-C6-494. �10.1051/jphyscol:1990658�. �jpa-00230928�
COLLOQUE DE PHYSIQUE
C o l l o q u e C6, s u p p l e m e n t
au
n022, Tome 51, 15 novembre 1 9 9 0THE IMPORTANCE OF POLARIZATION IN KAON PHOTOPRODUCTION AND RADIATIVE CAPTURE' )
S.R. COTANCH, R.A. WILLIAMS
and
CHUENG-RYONG JINorth C a r o l i n a S t a t e U n i v e r s i t y , Department of P h y s i c s , R a l e i g h , North C a r o l i n a 27695-8202,
U . S . A .A b s t r a c t
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Using a r e l a t i v i s t i c baryon resonance model c o n s t r a i n e d by c r o s s i n g and d u a l i t y , we s t u d y t h e e l e c t r o m a g n e t i c production of hyperons i n kaon photoproduction, y+
p + K ++
Y, and r a d i a t i v e c a p t u r e , K- -!- p + y+
Y, f o r Y = A , C and A(1405).D i s t i n c t s i g n a t u r e s a r e p r e d i c t e d f o r t h e d i f f e r e n t hyperon p o l a r i z a t i o n s which a r e d i r e c t consequences of SU(3) f l a v o r symmetry and p a r i t y c o n s e r v a t i o n . Other im- p o r t a n t r e s u l t s of o u r model a r e h i g h l i g h t e d .
1
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INTRODUCTIONIt i s e v i d e n t t h a t w i t h t h e advent of GeV e l e c t r o n a c c e l e r a t o r s , such a s CEBAF, new, funda- mental e l e c t r o m a g n e t i c s t u d i e s of n u c l e a r s t r u c t u r e and elementary r e a c t i o n mechanisms w i l l soon b e p o s s i b l e . One p a r t i c u l a r l y i n t e r e s t i n g c l a s s of r e a c t i o n s i s t h e e l e c t r o m a g n e t i c p r o d u c t i o n of hyperons. The hyperon masses (*1.0
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1.5 GeV) p l a c e t h e p r o d u c t i o n t h r e s h o l d a t a n i n t e r m e d i a t e energy where b o t h hadronic and QCD i n s p i r e d models have q u e s t i o n a b l e v a l i d i t y . The c u r r e n t t h e o r e t i c a l u n c e r t a i n t i e s a r e f u r t h e r hampered by t h e a v a i l a b l e d a t a which i s l i m i t e d i n b o t h q u a n t i t y and q u a l i t y . This s i t u a t i o n w i l l b e remedied by CEBAF which w i l l a l s o p e r m i t , i n connection w i t h t h e hyperon weak decay mechanism, " s e l f analyz- ing" p o l a r i z a t i o n measurements. A s d e t a i l e d below, p o l a r i z a t i o n experiments a r e e s p e c i a l l y important f o r developing our understanding of hyperon p r o d u c t i o n because t h i s o b s e r v a b l e i s v e r y s e n s i t i v e t o resonances included i n t h e amplitude. Although p r e c i s i o n d a t a may b e a few y e a r s away, a meaningful phenomenological a n a l y s i s of e x i s t i n g d a t a i s s t i l l c u r r e n t l y p o s s i b l e by comprehensively t r e a t i n g d i f f e r e n t o b s e r v a b l e s i n s e v e r a l r e a c t i o n c h a n n e l s w h i l e c o n s i s t e n t l y i n c o r p o r a t i n g dynamic symmetry p r i n c i p l e s (such a s c r o s s i n g and d u a l i t y ) t o f u r t h e r r e s t r i c t t h e model. I n t h i s paper, we p r e s e n t one such model which i s used t o d e s c r i b e t h e e l e c t r o m a g n e t i c production of A, Z and A(1405) hyperons. Our model, which i n c o r p o r a t e s d u a l i t y and c r o s s i n g symmetry, reproduces a l l e x i s t i n g kaon photoproduction and r a d i a t i v e c a p t u r e d a t a f o r t h e A and Z w h i l e making s e v e r a l i n t e r e s t i n g p r e d i c t i o n s f o r A(1405) production. The A and C a r e p r e d i c t e d t o be photoproduced w i t h o p p o s i t e p o l a r i z a - t i o n s a s a r e s u l t of t h e i r d i f f e r e n t SU(3) i s o s p i n s t r u c t u r e . We a l s o f i n d t h a t f o r t h e odd p a r i t y A(1405) t h e p o l a r i z a t i o n i s suppressed due t o p a r i t y c o n s e r v a t i o n and t h e dominance of even p a r i t y diagrams i n our model.2
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DETAILS OF THE MODELOur approach is based upon an e f f e c t i v e c h i r a l Lagrangian ( c a l c u l a t e d a t t h e t r e e - l e v e l ) i n which we i n c l u d e coupling t o a l l hadrons n e c e s s a r y t o a c h i e v e a r e a s o n a b l e d e s c r i p t i o n of t h e a v a i l a b l e A and C photoproduction c r o s s s e c t i o n and p o l a r i z a t i o n d a t a . Also, f o r con- s i s t e n c y w i t h c r o s s i n g symmetry, we r e q u i r e our model t o simultaneously f i t t h e new experi- mental v a l u e s f o r t h e kaon c a p t u r e branching r a t i o s . Our model is c o n s t r a i n e d f u r t h e r by adhering t o t h e d u a l i t y p r i n c i p l e which excludes a l l v e c t o r kaon exchanges from t h e model
(?)Supported i n p a r t by t h e U. S. Department of Energy, C o n t r a c t No. DE-FG05-88ER40461.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990658
C6-492 COLLOQUE DE PHYSIQUE
( s p i n 1 and h i g h e r resonances and meson exchanges produce a n unphysical h i g h energy de- pendence i n t h e p r o d u c t i o n amplitude). The h i g h energy behavior of a d u a l i t y c o n s i s t e n t model i s more a p p r o p r i a t e t h a n t h a t provided by i n t e r f e r e n c e modelsand t h e r e f o r e o u r model can b e a p p l i e d t o a wider kinematic r a n g e ( 1 ) . We have determined t h a t f o r A production seven diagrams a r e s u f f i c i e n t (p, N(1650) and N(1710) i n t h e s channel; A, C and A(1405) i n t h e U channel; K i n t h e t channel) w h i l e f o r
X
production two a d d i t i o n a l diagrams ( i n - v o l v i n g t h e A(1620) and A(1900)) i n t h e s channel a r e r e q u i r e d . With t h i s model, supple- mented by t h e o r e t i c a l i n p u t f o r A(1405) parameters (anomalous magnetic moment computed from t h e quark model; KN*Y coupling c o n s t a n t s c o n s t r a i n e d by symmetry arguments), we t h e n p r e d i c t t h e A(1405) photoproduction and c a p t u r e c r o s s s e c t i o n s and p o l a r i z a t i o n s . For f u r t h e r d e t a i l s of t h e c a l c u l a t i o n s e e r e f . 2.3
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RESULTS AND CONCLUSIONSFigs. 1 and 2 i l l u s t r a t e t h e A , C p o l a r i z a t i o n s and C p r o d u c t i o n c r o s s s e c t i o n , r e s p e c t i v e l y . Notice t h a t o u r model p r e d i c t s t h e C p o l a r i z a t i o n (no a v a i l a b l e d a t a ) i s l a r g e and o p p o s i t e t o t h e A p o l a r i z a t i o n . We f i n d t h a t t h i s o p p o s i t e p o l a r i z a t i o n i s a consequence of t h e d i f f e r e n t i s o s p i n s t r u c t u r e e x h i b i t e d by t h e s e s t a t e s , which produce r e l a t i v e s i g n d i f f e r e n - c e s i n t h e i r s t r o n g and e l e c t r o m a g n e t i c c o u p l i n g s t o t h e o t h e r hadrons. The dynamic s i g n i - f i c a n c e of t h e d i f f e r e n t A and Z i s o s p i n s t r u c t u r e i s f u r t h e r demonstrated i n f i g . 2 where t h e e f f e c t of two d e l t a graphs a r e s e e n t o have a s u b s t a n t i a l e f f e c t on t h e C photoproduc- t i o n c r o s s s e c t i o n , whereas because t h e A h a s i s o s p i n 0 , i t cannot couple t o t h e d e l t a s . The A(1405) p o l a r i z a t i o n i s found t o be s m a l l i n t h e e n t i r e kinematic r a n g e of v a l i d i t y f o r t h i s model (photon energy from t h r e s h o l d up t o Q2.0 GeV). T h i s s u p p r e s s i o n of t h e A(1405) p o l a r i z a t i o n a r i s e s due t o p a r i t y c o n s e r v a t i o n a c t i n g i n a model which i s dominated by even p a r i t y diagrams. The A(1405) has n e g a t i v e p a r i t y and t h u s p a r i t y c o n s e r v a t i o n s e l e c t s o u t t h e f i n a l s t a t e S-wave p a r t i a l wave component of t h e amplitude which dominates over p waves f o r e n e r g i e s n e a r t h r e s h o l d . However, t o produce a non-zero p o l a r i z a t i o n p wave amplitudes a r e needed and t h e r e f o r e t h e p o l a r i z a t i o n i s s m a l l n e a r t h r e s h o l d . It i s p o s s i b l e t h a t resonances which a r e n o t important f o r A and C production may b e s i g n i f i c a n t f o r A(1405) p r o d u c t i o n ( e s p e c i a l l y a t h i g h e r e n e r g i e s ) , i n which c a s e t h e a c t u a l A(1405) p o l a r i z a t i o n may n o t be small. However, based on t h e assumption t h a t A, C and A(1405) production can a l l b e d e s c r i b e d by t h e same s e t of resonances, a s m a l l p o l a r i z a t i o n f o r t h e A(1405) i s a f i r m p r e d i c t i o n of t h i s model. Other important r e s u l t s o b t a i n e d from t h i s model i n c l u d e : 1 ) ex- t r a c t i n g limits on t h e t r a n s i t i o n moment r a t i o f o r A(1405) + A
+
y t o C+
y of -0.21 f. 0.08 which s h a r p l y c o n t r a s t s t h e SU(3) p r e d i c t i o n +J3, i n d i c a t i n g t h e A(1405) i s c l e a r l y n o t an SU(3) s i n g l e t ) ; 2) p r e d i c t i o n of c r o s s s e c t i o n s t h a t a r e measurable f o r ~ ( y , ~ + ) A ( 1 4 0 5 ) b u t s m a l l , probably unmeasurable, f o r p(K-, y)A(1405) ( f i g s . 3 and 4 ) .Fig. 1
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A and C p o l a r i z a t i o n s n e a r t h r e s h o l d a t OCsm. Q 90'.I c.m. cross section
Fig. 2
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The importance of A c o n t r i b u t i o n s f o r t h e energy dependence of C photoproduction.The s o l i d l i n e i s t h e f u l l r e s u l t whereas t h e dash-dot l i n e i s c a l c u l a t e d without A c a l c u l a t i o n s .
c.m. cross section
da/dQ 5-1.6 GeV
F i g . 3
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A(1405) photoproduction c r o s s s e c t i o n a t E = 1.6 GeV showing t h e s e n s i t i v i t y t o Yt h e unconstrained parameters ( s o l i d l i n e f o r g mA(1405)= 1.5; dash-dot l i n e f o r gmA(1405)= 3.0). Dotted l i n e demonstrates s e n s i t i v i t y t o N* resonances (gmA(1405)
= 1.5 and N* coupling c o n s t a n t s s e t e q u a l t o z e r o ) .
COLLOQUE DE PHYSIQUE
P(K-*Y)Y
25 I I I I
cam. cross section I
Fig. 4
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I n f l i g h t c a p t u r e c r o s s s e c t i o n s a t 0 = 90' f o r A, C, and A(1405) a s a f u n c t i o nof t h e kaon l a b momentum. c.m.
I n summary, f u t u r e copious and a c c u r a t e d a t a from kaon f a c t o r i e s and electromagnetic f a c i - l i t i e s , such a s CEBAF, should provide new and deeper understanding of b o t h hyperon s t r u c t u r e and t h e elementary mechanism f o r hyperon production. To a c h i e v e t h i s g o a l w i l l r e q u i r e a comprehensive, c o n s i s t e n t approach involving a complete a n a l y s i s of m u l t i - r e a c t i o n channels and a l l p h y s i c a l o b s e r v a b l e s , e s p e c i a l l y p o l a r i z a t i o n .
REFERENCES
/l/ Y. Renard, Nucl. Phys.
E ,
499 (1971)./ 2 / R. Williams, C.-R. 31 and S. R. Cotanch, Phys. Rev.
