REVIEW OF Λ° AND Λ-° POLARIZATION MEASUREMENTS AT THE CERN - ISR

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REVIEW OF Λ° AND Λ-° POLARIZATION MEASUREMENTS AT THE CERN - ISR

P. Schlein

To cite this version:

P. Schlein. REVIEW OFΛ° AND Λ-° POLARIZATION MEASUREMENTS AT THE CERN - ISR.

Journal de Physique Colloques, 1985, 46 (C2), pp.C2-131-C2-140. �10.1051/jphyscol:1985213�. �jpa- 00224524�

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Colloque C2, supplément au n°2, Tome 46, février 1985 page C2-131

REVIEW OF A° AND A° POLARIZATION MEASUREMENTS AT THE CERN - ISR

P.E. Schlein

University of California, Los Angeles, U.S.A.

Résumé - Les mesures de polarisation des A0 et A0 faites au CERN-ISR.

Concernent ( i ) la production inclusive des A0 dans les interactions p p ; ( i i ) Un t e s t de l ' i n v a r i a n c e CP u t i l i s a n t les A0 des i n t é r a c t i o n s pp et les A0 des inte'ractions p p ; ( i i i ) la première observation de la polarisation dans les processus d i f f r a c t i f s . Nous indiquons e'galement les t r a v a u x en cours avec les donne'es de l'expérience R608.

A b s t r a c t - A0 and A0 Polarization measurements at t h e CERN-ISR are summarized. These a r e : ( i ) i n c l u s i v e AD's f r o m p p i n t e r a c t i o n s , ( i i ) CP- invariance t e s t using A0 from pp and A0 from p p i n t e r a c t i o n s , and ( i i i ) the f i r s t o b s e r v a t i o n of polarization in d i f f r a c t i v e processes. Work in progress w i t h data f r o m experiment R608 is also summarized.

Polarization measurements have been made in two experiments at t h e CERN I n t e r s e c t i n g Storage R i n g s , R603 and RG08. In t h i s t a l k I review the results of both and also summarize the polarization w o r k in t h e ongoing data analysis of the R608 g r o u p .

T h e e x i s t i n g w o r k appears in t h r e e papers / 1 , 2 , 3 / . In t h e f i r s t paper (from experiment R603), Erhan et a l . / I / s t u d i e d t h e inclusive p r o d u c t i o n of A0 in pp interactions w i t h Vs = 53 and 62 GeV:

PP - A° • X (1) and f o u n d t h a t t h e A ° ' s were polarized by as much as -40% f o r t r a n s v e r s e

momentum P. > 1 G e V / c along the normal t o the p r o d u c t i o n p l a n e , n ~ p* x A . T h i s r e s u l t was t h e f i r s t from high e n e r g y pp interactions and showed t h a t t h e polarized A ° ' s o b s e r v e d by the Michigan-Rutgers-Wisconsin collaboration in p-Be interactions at Fermilab had l i t t l e , if a n y t h i n g , t o do w i t h t h e nuclear t a r g e t and was essentially a consequence of t h e p r o t o n f r a g m e n t a t i o n mechanism.

In the second paper (from R608), Chauvat et a l . 7 2 / showed t h a t the A ° ' s in Reaction (1) had t h e same polarization as t h e ( i n c l u s i v e ) A ° ' s in t h e Reaction:

p p - A° • X , (2) both w i t h Vs = 31 GeV. In Reaction ( 2 ) , t h e A ° ' s are in t h e direction of the

i n c i d e n t p's. As explained below, t h i s simultaneously tests C-invariance and f a c t o r i z a t i o n in p p interactions a n d , what is perhaps most i n t e r e s t i n g , CP- invariance in A0 d e c a y .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985213

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Finally, i n t h e t h i r d p a p e r ( f r o m R6081 E r h a n e t al. /3/ r e p o r t e d a polarization measurement on t h e A O ' s p r o d u c e d i n t h e e x c l u s i v e d i f f r a c t i v e reaction:

w i t h V s = 62 GeV. T h i s is most i n t e r e s t i n g because t h e p r o d u c t i o n mechanism i s simpler a n d because t h e A O ' s a r e p r o d u c e d d i r e c t l y w i t h n o intermediate 1 ° , Z

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*

F i g u r e 1

MASS (p r') MeV

F i g u r e 1 shows a A D signal t y p i c a l o f b o t h experiments.

-

'wire Chomben B

z (melersl F i g u r e 2

F i g u r e 2 is a l a y o u t d r a w i n g of t h e R608 f o w a r d spectrometer /4/.

It was similar i n conception t o t h e o r i g i n a l R603 spectrometer i n t h a t it was a device designed t o d e t e c t a n d i d e n t i f y f o r w a r d g o i n g m u l t i - p a r t i c l e systems. T h e d e t e c t o r

was i n s t a l l e d o n a n o u t - g o i n g beam p i p e i n i n t e r s e c t i o n - 6 o f t h e I S R . T h e d e v i c e c o n s i s t e d e s s e n t i a l l y o f t w o i n d e p e n d e n t magnetic spectrometers, o n e p o s i t i o n e d a b o v e t h e beam p i p e a n d o n e below. F i g u r e 3 shows a f r o n t a l v i e w o f t h e magnetic

a p e r t u r e ( l o o k i n g downstream) a n d i l l u s t r a t e s t h e s p a t i a l r e l a t i o n s h i p between t h e

"UP" a n d "DOWN" spectrometers.

T h e h a t c h e d a r e a i s a septum p l a t e w h i c h s h i e l d e d t h e c i r c u l a t i n g ISR beams ( t y p i c a l l y 3 0 Amperes o f p r o t o n s i n R608) f r o m t h e magnetic f i e l d . T h e magnetic f i e l d i s i n t h e same d i r e c t i o n i n b o t h UP a n d DOWN spectrometers. T h i s has t h e consequence t h a t A O ' s i n t h e UP s p e c t r o m e t e r t y p i c a l l y h a v e t h e i r n o r m a l - t o - t h e - p r o d u c t i o n - p l a n e , n, t o t h e r i g h t , as shown, w h i l e n i s i n t h e o p p o s i t e sense f o r A O ' s i n t h e DOWN s p e c t r o m e t e r . Since t h e magnetic b e n d i n g i s t h e same b o t h UP a n d DOWN, t h e acceptance c o r r e c t i o n s a r e v a s t l y d i f f e r e n t ( w i t h r e s p e c t t o n ) f o r t h e t w o sets o f d a t a . T h i s p r o v i d e d us, i n b o t h R603 a n d R608, w i t h a n i m p o r t a n t v e r i f i c a t i o n o f o u r r e s u l t s , because t h e measured p o l a r i z a t i o n s m u s t a g r e e i n t h e t w o cases.

I n b o t h e x p e r i m e n t s t h e i n c l u s i v e t r i g g e r demanded o n l y t h a t t r a c k s t r a v e r s e d t h e spectrometer, a l t h o u g h f o r t h e d i f f r a c t i v e d a t a d i s c u s s e d below, t h e r e was a s u p p l e m e n t a r y c o n d i t i o n w h i c h vetoed e v e n t s w h i c h h a d a d d i t i o n a l p a r t i c l e s i n t h e c e n t r a l r e g i o n . I n n o case was a n y a t t e m p t made t o select e v e n t s w i t h s t r a n g e p a r t i c l e s i n r e a l t i m e . T h i s selection was done o f f - l i n e ; t y p i c a l l y 2-3% o f a l l e v e n t s c o n t a i n e d a r e c o n s t r u c t e d A 0 ( o r

p

0

F i g u r e 4 shows a t y p i c a l scatter p l o t i n t h e v e r t i c a l plane o f A 0 decay v e r t i c e s from, i n t h i s case, R603.

T h e e f f e c t o f t w o i n d e p e n d e n t acceptance a p e r t u r e s i s c l e a r l y seen. I n R603 t h e a n g u l a r a p e r t u r e f o r i n d i v i d u a l t r a c k s was 15-90 mrad, w h i l e i n R608 t h e a p e r t u r e was 23-150 m r a d . A n ' s selected f o r a n a l y s i s w e r e t y p i c a l l y r e q u i r e d t o h a v e a v e r t e x more t h a n 2 0 cm downstream f r o m t h e i n t e r s e c t i o n o f t h e A 0 v e c t o r a n d t h e h o r i z o n t a l beam-beam i n t e r s e c t i o n plane.

F i g u r e 3

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F i g u r e 4

01 I I I I I I

2 6 40 14 18 22 26

Longitudinal Momentum (GeV/c) F i g u r e 5

F i g u r e 5 shows t h e PI v s . Pt d i s t r i b u t i o n f o r t h e V s = 53 GeV AO sample used i n reference / l / , o n w h i c h several c o n s t a n t acceptance c o n t o u r s a r e superimposed.

The o u t e r b o u n d a r i e s approximately c o r r e s p o n d t o t h e 15 and 90 m r a d a p e r t u r e limits. Corrected A 0 d i f f e r e n t i a l cross sections f r o m t h i s data sample have been p u b l i s h e d i n another p a p e r b y E r h a n e t al. /5/.

- _{non-A0 n-Q} -

0. I

-

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- 60 - 26/26 GeV

0

31/31 GeV

F i g u r e 6

T h e f i n a l p o l a r i z a t i o n r e s u l t s f r o m R603 / l / a r e seen i n F i g u r e 6. T h e h i g h e r s t a t i s t i c s o f t h e 26/26 GeV data show t h a t t h e p o l a r i z a t i o n increases w i t h Pt. A n a d d i t i o n a l v e r i f i c a t i o n o f t h e r e s u l t s i s also shown i n t h i s F i g u r e as t h e p o i n t l a b e l l e d " n o n - A o R-p". T h i s i s t h e p o l a r i z a t i o n e v a l u a t e d f o r R-p p a i r s w h i c h a r e n o t Ao; t h e y a r e chosen i n t w o mass b i n s o n e i t h e r s i d e o f t h e A 0 p e a k a n d h a v e v e r t i c e s i n t h e beam - beam c r o s s i n g r e g i o n . T h e " p o l a r i z a t i o n " o f t h e s e e v e n t s i s zero, as expected.

We t u r n now t o t h e p a p e r o f C h a u v a t e t al. /2/ i n w h i c h Reactions 1 a n d 2 a r e compared. C - i n v a r i a n c e i n Reaction (2) says t h a t An's o b s e r v e d i n t h e (opposite) beam-proton a r m o f t h e same reaction:

s h o u l d have i d e n t i c a l p o l a r i z a t i o n as t h e x O ' s i n Reaction 2. T h u s , a comparison b e t w e e n Reactions 1 a n d 2 is, i n essence, a comparison between A O ' s i n Reactions 1 a n d 4. " A r m - A r m F a c t o r i z a t i o n " i n t h e s e t w o reactions, namely independence o f s e c o n d a r y p a r t i c l e p r o p e r t i e s i n p-X o n w h e t h e r t h e t a r g e t i s p o r p is f o u n d t o b e v a l i d t o w i t h i n t h e f e w p e r c e n t level.

T h e actual comparison o f data i n t h e p p Reaction 1 a n d t h e p p Reaction 2 i s f a c i l i t a t e d by t h e f a c t t h a t t h e magnetic f i e l d was set o p p o s i t e in t h e t w o cases.

T h u s , t h e r a w i n c l u s i v e momentum d i s t r i b u t i o n s c a n b e d i r e c t l y compared w i t h o u t t h e n e e d f o r s i g n i f i c a n t geometric o r e f f i c i e n c y c o r r e c t i o n s .

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Figure 7

F i g u r e 7 shows t h e comparison between c h a r g e d p a r t i c l e a n d A o ( A o ) data i n Reactions 1 a n d 2 a t V s = 31 GeV. P a r t (a) compares ( p

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--

T h e s e d i f f e r e n c e s can b e u n d e r s t o o d as a r e s u l t o f q q a n n i h i l a t i o n processes i n t h e pp i n t e r a c t i o n . Simple q u a r k c o u n t i n g p r e d i c t s t h a t u z a n n i h i l a t i o n i s f o u r times more l i k e l y t h a n d z a n n i h i l a t i o n . T h i s leads t o a m o d i f i c a t i o n o f t h e p r o b a b i l i t i e s t o f i n d u u a n d u d d i q u a r k s a n d hence t o d i f f e r e n c e s o f p r o d u c t i o n o f states l i k e A + + a n d A o i n p p a n d pp i n t e r a c t i o n s . I n a n o t h e r C h a u v a t e t al. p a p e r / 6 / , these effects a r e o b s e r v e d a n d discussed i n some detail a n d I t h e r e f o r e w i l l n o t s a y more on t h e s u b j e c t i n t h i s t a l k .

A t t h e mean PI of t h e A O ' s a n d x o ' s used i n t h e comparison, -9 GeV/c, F i g u r e 7 shows n e g l i g a b l y small d i f f e r e n c e s a n d it is t h e r e f o r e l i k e l y t h a t t h e A n ' s . i n Reaction 1 a n d t h e T o ' s i n Reaction 2 have t h e same polarization - a t least t o w i t h i n t h e s t a t i s t i c a l u n c e r t a i n t i e s o f t h e aP measurements.

Transverse Momentum (p,) GeV/c F i g u r e 8

F i g u r e 8 shows t h e r e s u l t i n g values o f polarization p l o t t e d v s . Pt f o r t h e t w o samples o f data. I n t h e Figure, t h e measured q u a n t i t y aP is d i v i d e d by t h e known magnitude o f a,, i n each case. Since C P - i n v a r i a n c e i n A 0 decay r e q u i r e s a t o have o p p o s i t e s i g n f o r p a r t i c l e a n d anti-particle, t h e p l o t t e d q u a n t i t y s h o u l d b e m i r r o r

-

symmetric if C P - i n v a r i a n c e is v a l i d ( a n d if t h e AD, A D polarizations a r e identical).

T h e p l o t t e d values o f a P / l a A ( a r e g i v e n i n t h e following T a b l e I along w i t h t h e i r mean values a n d t h e value f o r n o n - h a IT-p systems. T h e l a t t e r values a r e compatible w i t h zero, as required, w h i l e t h e mean values a r e (15.5t2.7)% f o r p-AD a n d (+16.1+3.6)% f o r p - 3 . T h i s r e s u l t c o n s t i t u t e s t h e f i r s t observation o f p o l a r i z e d A o ' s a n d is also t h e f i r s t t e s t o f CP-invariance i n A D decay.

1 1

I ^{TABLE I A O AND}

70

I I

I Selection pp (15/15 Gev) pp (15/15 Gev) I

I I

I pt = 0.4-0.6 Gev/c 4.2 + 4.0 -3.1 + 3 . 1 I

I 0.6-0.8 1 1 . 7 t 4.7 -9.9 t 3.5 I

I 0.8-1 .O 19.2 t 6.7 -17.9 t 4 . 9 I

I 1 .O-1.4 30.7 t 10.5 -35.3 t 7.5 I

I I

I 0.6-1.4 (all) 16.1 + 3 . 6 -15.5 + 2.7 I

I I

I 0.6-1.4 (non-/\) 2.1 ^t 4.6 3 . 0 ^t 3.8 I

I I

1 (a) q u a n t i t i e s shown a r e measured values o f aAPA d i v i d e d I

I b y t h e absolute value o f a.,, t

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T h e l a s t p a p e r t o b e d i s c u s s e d i s t h e o n e /3/ w h i c h r e p o r t s p o l a r i z a t i o n i n d i f f r a c t i v e d i s s o c i a t i o n p p

-

Total Momentum G e ~ / c

F i g u r e 9

e v e n t s w i t h Ptot i n t h e r a n g e 30-33 GeV/c o f t h e x F = 1 p e a k u s e d f o r t h i s a n a l y s i s . T h e t a i l below t h e p e a k m o s t l y c o n t a i n s e v e n t s w h i c h a r e p

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w i t h t h e no missing a n d do n o t concern u s h e r e . T h e small b a c k g r o u n d f r o m t h i s s o u r c e i n t h e s e l e c t e d 30-33 GeV/c p e a k r e g i o n has been shown t o cause n o s i g n i f i c a n t m o d i f i c a t i o n o f o u r p o l a r i z a t i o n r e s u l t . F i g u r e 10 shows t h e A ° K + i n v a r i a n t mass f o r t h e p e a k e v e n t s u s e d f o r t h e p o l a r i z a t i o n measurement.

A l t h o u g h t h e r e i s some evidence f o r resonance p r o d u c t i o n , p

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* -

F i g u r e 11 shows t h e a c c e p t a n c e - c o r r e c t e d A 0 decay d i s t r i b u t i o n w i t h t h e b e s t fit c o r r e s p o n d i n g t o a polarization o f (-36.1+4.5)% f o r t h e xF-Pt r e g i o n (0.5-0.8) a n d (0.5-1.5) GeV/c w h e r e t h e r e a r e 3190 e v e n t s . T h e s e a r e t h e e v e n t s w i t h t h e b e s t acceptance. T h e r e i s n o e v i d e n c e f o r moments w i t h L > 1 a n d t h e p o l a r i z a t i o n r e s u l t s f o r e v e n t s i n t h e UP a n d DOWN spectrometers a r e -37% a n d -35%, r e s p e c t i v e l y .

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F i g u r e 10

F i g u r e 11

F i n a l l y , we come t o t h e w o r k i n p r o g r e s s . A l l p o l a r i z a t i o n analyses t h a t we h a v e r e p o r t e d u n t i l now f o r b o t h e x p e r i m e n t s R603 a n d R608 h a v e u s e d A 0 e v e n t samples of, t y p i c a l l y , 5000-10000 e v e n t s b e f o r e PI-Pt selections. T h e q u o t e d p o l a r i z a t i o n e r r o r s a r e u s u a l l y 3-5%. It i s t h e r e f o r e i n t e r e s t i n g t o note t h a t t h e t o t a l R608 data sample contains a b o u t 3 million r e c o n s t r u c t e d A o ' s a n d s150,OOO T o ' s .

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A p p r o x i m a t e l y o n e - h a l f t h e A n sample is f r o m i n c l u s i v e t r i g g e r s a n d o n e - h a l f f r o m d i f f r a c t i v e t r i g g e r s ( m o s t l y p

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Dependences o n PI a n d Pt ? I s t h e r e a dependence on s ?

I s A 0 p o l a r i z a t i o n g r e a t e r , i n e i t h e r d i f f r a c t i v e o r i n c l u s ~ v e p r o d u c t i o n , when measured w i t h r e s p e c t t o t h e A ° K + p l a n e r a t h e r t h a n t h e A n p r o d u c t i o n p l a n e ? A r e An's f r o m p p i n t e r a c t i o n s p o l a r i z e d a t ISR e n e r g i e s ?

.

Detailed comparison o f A 0 p o l a r i z a t i o n i n i n c l u s i v e a n d d i f f r a c t i v e channels.

Can l o n g i t u d i n a l A n polarization, < o p>, b e e f f e c t i v e l y u s e d as a p r o b e o f h e a v y f l a v o r decay ?

How does A 0 p o l a r i z a t i o n d e p e n d o n o t h e r r e a c t i o n p r o p e r i t e s s u c h as n e a r b y p a r t i c l e s , m u l t i p l i c i t y , etc. ?

REFERENCES

/l/ S. E r h a n e t al., Phys. L e t t e r s 828, 301 (1979)

/2/ P. C h a u v a t e t al, CERN-EP/83-104, EPS Conference, B r i g h t o n (1983) a n d t o b e p u b l i s h e d .

/3/ S . E r h a n e t al., CERN-EP/84-84, Proceedings o f L u n d M u l t p a r t i c l e Symposium ( i n press-1984)

/4/ P. C h a u v a t e t al., CERN-EP/82-198, P a r i s C o n f e r e n c e (1982) a n d Proceedings o f t h e 1983 Workshop o n Collider Detectors, LBL-15973.

/ 5 / S . E r h a n e t al., Phys. L e t t e r s 85B, 447 (1979).

/6/ P. C h a u v a t e t a l . , P h y s . L e t t e r s 1278, 384 (1983).