POLARIZED TARGET RESULTS

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POLARIZED TARGET RESULTS

W. Beusch

To cite this version:

W. Beusch. POLARIZED TARGET RESULTS. Journal de Physique Colloques, 1973, 34 (C1), pp.C1- 296-C1-297. �10.1051/jphyscol:1973137�. �jpa-00215217�

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W. BEUSCH

POLARIZED TARGET RESULTS

W. BEUSCH CERN

A t p r e v i o u s c o n f e r e n c e s , p o l a r i z a t i o n r e s u l t s have been r e p o r t e d on e l a s t i c s c a t t e r i n g (up t o 16 GeV/c), o n charge exchange and on i n e l a s t i c two-body r e a c t i o n s where t h e f i n a l s t a t e baryon i s a hyperon t h a t c a r r i e s i t s own p o l a r i z a t i o n a n a l y s i s i n i t s weak decay, There h a s been c o n s i d e r a b l e p r o g r e s s i n t h e werk of e x p e r i m e n t a l i s t s . Measurements have been extended t o 40 GeV/c and t o K- , nucleon and a n t i - nucleon c h a r g e exchange

.

^{A s}a n example, a n t i p r o t o n s c o n s t i t u t e about 0.5% of t h e beam and c h a r g e exchange i s about 5% a s f r e q u e n t a s e l a s t i c s c a t t e r i n g . Such measurements have become p o s s i b l e by a c o n s i d e r a b l e p r o g r e s s [ I , 2 ] i n p o l a r i z e d t a r g e t technique, and by n o t observing t h e r e c o i l nucleon making p o s s i b l e a l a r g e a p p a r a t u s acceptance.

Measurements of t h e p o l a r i z a t i o n parameter P and t h e s p i n r o t a t i o n parameter R have been completed r e c e n t l y a t t h e Serpukhov a c c e l e r a t o r [3]. ^TWO m i l - l i o n e l a s t i c c o u n t s (50% of t h e i r d a t a ) have gone i n t o f i g . 1 . The p o l a r i z a t i o n i n t h e r e g i o n

- ^{ref 4}

ra G+/C --- ^ref5

---- ^ref⁶

... ^{ref 7}

I

_Fig.₁

- ^.5 ^>^t^>-1 ( ~ e ~ / c ) ~ is compatible with being zero;

i t remains small a t l a r g e r It 1 . The p r e d i c t i o n s of v a r i o u s models [4.. .71 a r e i n g e n e r a l compatible w i t h

t h e s e new d a t a . The same agreement i s found w i t h t h e p r e l i m i n a r y d a t a on R i n 72 - p e l a s t i c s c a t t e r i n g a t 40 GeV/c ( s e e f i g . 2 ) . R i s a l s o compatible w i t h t h e c o s i n e of t h e c.m.s. a n g l e of t h e p r o t o n r e c o i l , a s expected i f t h e s-channel h e l i c i t y f l i p amplitude i s zero. T h i s h a s a l r e a d y been observed i n previous measurements a t 6 and 16 GeV/c [ 8 1 .

F i r s t r e s u l t s on P i n K-p e l a s t i c s c a t t e r i n g have been p r e s e n t e d by t h e same group : s e e fig.3.

The p o l a r i z a t i o n i s very small ( i t s s i g n i s a c t u a i - l y not d e f i n e d ) up t o t = -0.2 (GeV/c) 2

.

From t=-0.2 t o -0.8 ( G ~ v / c ) ~ P i s p o s i t i v e and smoothly i n c r e a - s i n g ,

Fig.3

Comparing t h e s e r e s u l t s w i t h p r e v i o u s CERN d a t a one c a n deduce t h e s-dependence of P ( s e e r a p p o r t e u r ' s r e p o r t by U. Amaldi). I n g e n e r a l , t h e s e d a t a a r e n o t i n disagreement w i t h c u r r e n t Regge p o l e models which have been adapted t o f i t t h e d a t a a t lower energy.

The f i r s t measurement of t h e p o l a r i z a t i o n parame- t e r P i n K-p charge exchange was p r e s e n t e d t o t h i s con'ference [91

.

^As ^p ^{and A2} exchange a r e expected t o dominate t h i s p r o c e s s , many p r e d i c t i o n s have been made, based on o t h e r r e a c t i o n s where p and A a r e involved (mainly YP ^-tnon and xmp ^rln).

2

I n p r e - d u a l i t y t i n e s a l a r g e p o l a r i z a t i o n , p o s i t i v e

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1973137

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POLARIZED TARGET RESULTS

o r n e g a t i v e , was u s u a l l y p r a d i c t e d . Whereas s t r i c t exchange degeneracy p r e d i c t s a v a n i s h i n g p o l a r i z a - t i o n , more r e c e n t models i n c l u d i n g a b s o r p t i o n pre- d i c t e d a s m a l l b u t non-zero value. The r e s u l t s , to- g e t h e r w i t h a sample of r e c e n t p r e d i c t i o n s , a r e shown i n f i g u r e 4. Most p r e d i c t i o n s a r e i n r e a s o n a b l e agreement w i t h t h e d a t a . I was t o l d by t h e o r e t i c i a n s t h a t most model b u i l d e r s have profi-ted from SU(3) - ^{r e -}

l a t e d r e a c t i o n s , e.g. %+p + K+ 2' , where P h a s been measured.

P o l a r i z a t i o n measurements on np + pn and Gp ⁺- ⁿⁿ

have r e c e n t l y been p u b l i s h e d [11,12 1 . I n t h e np ⁴pn c a s e , t h e p o l a r i z a t i o n i s remarkably inde- pendent of s ; a f a c t a l r e a d y noted f o r t h e shape of t h e d i f f e r e n t i a l c r o s s - s e c t i o n . I n f i g . 5 t h e two

experiments (8 t o 1 0 GeV/c f o r np and 8 GeV/c f o r

- pp) a r e compared u s i n g t h e same s i g n c o n v e n t i o n ( f a s t i n c i d e n t x f a s t o u t g o i n g i n t h e Lab system). A t f i r s t s i g h t , t h e s i g n d i f f e r e n c e of P i n t h e s e two p r o c e s s e s , r e l a t e d by l i n e r e v e r s a l , might be thought of a s coming simply from a s i g n change o f a n a n p l i - t u d e under l i n e r e v e r s a l . A c t u a l l y t h e s i t u a t i o n is complicated h e r e and not t o o w e l l understood t h e o r e - t i c a l l y , s i n c e q u i t e a few amplitudes may be involved.

REFERENCES [I I ^BRUNETCW(c.) e t a l . , ~ h y s . L e t t e r s 448 (1973)471 [2 1 VERMEULEN (J. ), Proc. I n t . Conf. on P o l a r i z e d

T a r g e t s , LBL, (1971) p.69

[3 1 BRUNETON (C. ) e t a l . , IHER-ITEP-JINR-Saclay Col- l a b o r a t i o n , paper 431

151 GIRARDI (G.) e t a l . , Nucl. Phys. 047 (1972) 445 [6 1 ARAKELYAN (G. 1, paper p r e s e n t e d a t t h e 26th I n t .

Conf. on High Energy P h y s i c s , B a t a v i a , 1972 [7 1 GARSEVANISHVILI (V. ) e t a l . , JINP p r e p r i n t (1972) [ 8 1 DE LESQUEN (A.) e t a l . , Phys. L e t t e r s 40B (1972)

3.77

-. .

[ 9 ] BEUSCH (W. ) e t a l . , CERN-ETH-1.C.-Saclay C o l l a - b o r a t i o n , paper 214

[ l o ] The numbered c u r v e s a r e : (1) HOLDEN (J.P.) and ROBERTSON (D.C.), U n i v e r s i t y of Oregon p r e p r i n t ;

( 2 ) BLACKMON (M.L.) and GOLDSTEIN (G.R.), Phys.

Rev. 179 (1969) 1480 ; ( 3 ) and ( 5 ) RINGLAND (G.

A,), ROBERTS (R.G.), ROY (D.P.) and TRAN THANH VAN ( J . ) , Nucl. Phys. (1972) 395 ; ( 4 ) HARTLEY (B.J.) and KANE (G.L.), U n i v e r s i t y of Michigan, p r e p r i n t ( ~ a n u a r y 1973) ; ( 6 ) s e e r e f . 5 ; ( 7 ) 4 t h o r d e r polynomial

[11] ABOLINS (M.A.) e t a l . , Michigan S t a t e - Ohio S t a t e - C a r l e t o n - S t . Louis C o l l a b o r a t i o n , Phys.

Rev. L e t t e r s 2 (1973) 1183

[121 LE DU (P. ) e t a l . , CERN-ETH-1.C.-Saclay C o l l a - b o r a t i o n , Phys. L e t t e r s 44B (1973) 390.