c

Volume 38B, n u m b e r 4

PHYSICS

THE

REACTIONS K-p

LETTERS

K-p

-~ K * 5 ( 1 4 2 0 ) N

21 F e b r u a r y 1972

--* K * 5 ( 8 9 0 ) N AT

14.3

AND

GeV/c

B. C H A U R A N D , B. D R E V I L L O N . G. L A B R O S S E , D. L I N G L I N , R. A. S A L M E R O N Laborato~re de Physique NuclSazre des Hautes Energzes, Ecole Polytechnzque, Paros, France R. B A R L O U T A U D , A. B O R G , C. L O U E D E C , F. P I E R R E , M. S P I R O D~partement de Physique des Part~cules ElSmentazres, CEN, Saclay, France R. J. M I L L E R , J . J P H E L A N a n d T. P . SHAH Rutherford H~gh Energy Laboratory~ Chillon, D~dcot, UK Received 17 J a n u a r y 1972

P r e l i m i n a r y r e s u l t s are presented on K*(890) and K*(1420) production in t h r e e - b o d y final states of 14.3 GeV/c K-p interactions. F o r K*°(890) production, the total and differential c r o s s - s e c t i o n s and the density m a t r i x e l e m e n t s are d e t e r m i n e d . The K*- reaction is found to be dominated by natural parity exchange and the charge exchange reaction by unnatural parity exchange. The total c r o s s sections are given for K*~(1420) productton. W e h a v e s t u d i e d K* p r o d u c t i o n a t 14.25 + 0.10 G e V / c in t h e f o l l o w i n g r e a c t i o n s : K-p~K°~-p

seen

K-p ~ ~o u-p

unseen

K - p ~ K - ~Op, K-p ~K-

~+n,

and

~-o ~o

(la) (lb) (2)

D a h t z p l o t f o r t h e s e e v e n t s , d i s p l a y e d in fig. 1, s h o w s few e v e n t s o u t s i d e t h e K * - ( 8 9 0 ) , K * - ( 1 4 2 0 ) a n d low m a s s N* b a n d s . N e v e r t h e l e s s in t h e ~-ou- m a s s d i s t r i b u t i o n , d i s p l a y e d in t h e s h a d e d h i s t o g r a m of fig. 2a, a s m a l l p e a k i s v i s i b l e n e a r 1800 M e V w h e r e a K* r e s o n a n c e h a s r e c e n t l y b e e n s u g g e s t e d [2]. A l s o f r o m t h i s f i g u r e

(3)

in a n e x p e r i m e n t u s i n g t h e C E R N 2 m h y d r o g e n b u b b l e c h a m b e r a n d R. F. s e p a r a t e d b e a m . T h e film has been double scanned and the scanning e f f i c i e n c y i s c l o s e to u n i t y e x c e p t f o r a few special configurations such as events with lowmomentum-transfer protons and with a fast negative track near the beam direction. The cross section basis for the experiment has been o b t a i n e d b y n o r m a l i z i n g t h e t o t a l n u m b e r of i n t e r a c t i o n s to K - p t o t a l c r o s s s e c t i o n of 2 1 . 5 + 0.2 m b [1]. A p p r o p r i a t e c o r r e c t i o n s h a v e been made for unobserved forward elastics and 0 - p r o n g e v e n t s a n d in e a c h t o p o l o g y f o r s c a n e l f i c i e n c y a n d e v e n t s l o s t in p r o c e s s i n g . T h e s e r e s u l t s a r e b a s e d on a p p r o x i m a t e l y 6.7 e v e n t s / p b f o r r e a c t i o n ( l a ) a n d 4.9 e v e n t s / g b f o r t h e other reactions, representing about one quarter of t h e f i n a l s t a t i s t i c s . K-p ~ K*-p. The 7-constraint reaction (la) y i e l d s a n u n a m b i g u o u s s a m p l e of 267 e v e n t s . T h e

2420.

K-p ~ R ° n--p =

25 GeVlc

16. M2(pn.~ 12 8-

4. o. M 2( R " n - )

(GeV 2 )

Fig. 1. DaIitz plot for the final state ~O~-p with obs e r v e d ~o decays (267 events).

253

Volume 38B, n u m b e r 4

PHYSICS

15C

LETTERS

21 F e b r u a r y 1972

EvE~Sp0;'E3R0~ :

004 GO/

1c 100 EVENTS PER 0 04 C~V

e ) m-p ~ ( K r r ) -p

V

1'2

1'e

z4

n --

-.Jim ,

O6

12

,

18

~

- m - m . m . .

mm..,mBL .

24 30 KT~ EFFECTIVE MASS (GeV)

m..

m

-

3'o

rl 36'

,-.PI u'-- I-r'J Jrl ] ~

4'2

,-i_ .

,

,

36

42

Fig. 2. a) The shaded h i s t o g r a m displays the K°Tr- effective m a s s for the ~o~.-p final state with observed ~o decay, weighted for unseen decays. The open h i s t o g r a m r e p r e s e n t s the ( K ~ - effective m a s s from both the kn~Tr-p (all events) and K-~°p h n a l states. The i n c r e a s e d background in the open h i s t o g r a m is p r i m a r i l y due to I = ½ N*'s in the 1~ ° combinatmn, a c o n t a m m a t m n contributing near the K*-(1420) is d i s c u s s e d in the text (2035 events), b) The K-y + effective m a s s d i s t r l b u t m n ~n the K-Tr+n final state (877 events) for events with m i s s i n g m a s s less than the neutron m a s s (see text). i t i s c l e a r t h a t t h e n u m b e r of b a c k g r o u n d e v e n t s u n d e r t h e K*(890) i s n e g l i g i b l e , a n d we e s t i m a t e t h a t t h e b a c k g r o u n d u n d e r the K*(1420) i s l e s s t h a n 10%. T h e c h a n n e l a n d K * - c r o s s s e c t i o n s , p r e s e n t e d in t a b l e 1, w e r e d e t e r m i n e d f r o m r e action (la), with appropriate wezghting_for the ~-o e s c a p e p r o b a b z h t y a n d f o r u n s e e n K ° d e c a y m o d e s $. In o r d e r to s t u d y K * - ( 8 9 0 ) p r o d u c t i o n in d e t a l l , t h e d a t a f r o m r e a c t i o n s ( l b ) a n d (2) h a v e b e e n a d d e d to t h a t of r e a c t i o n ( l a ) . S i n c e t h e r e a c t i o n s u n d e r c o n s z d e r a t l o n a r e p e r z p h e r a l in n a t u r e , r e a c t i o n s ( l b ) a n d (2) c a n a l m o s t a l w a y s b e d l s t m g m s h e d f r o m r e a c t i o n (3). H o w e v e r , r e a c t z o n s ( l b ) a n d (2) a r e u s u a l l y a m b i g u o u s w i t h e a c h o t h e r ; t h i s a m b i g u i t y w a s r e s o l v e d on t h e b a s i s of k m e m a t z c h t p r o b a b i l i t y . T h i s s e p a r a t i o n i s u m m p o r t a n t i n s o f a r a s a s t u d y of t h e Table 1 Reaction c r o s s sections Reaction

254

C r o s s section ~b

K-p ~ ~Oy-p

155 ± 15

K-p ~ K-~'°p

190 =L40

K-p ~ K-~'+n

315 -e 45

K-p ~ K*-(890)p

119 ~=18

K-p ~ K*-(1420)p

77 • 12

K-p ~ K*°(890)n

61 ± 15

K-p ~K*°(1420)n

48 ± 20

K*(890) d i f f e r e n t i a l c r o s s s e c t i o n t s c o n c e r n e d since the proton is usually well measured and t h u s d e t e r m i n e s t h e m o m e n t u m t r a n s f e r to t h e t a r g e t p r o t o n a n d t h e K~ e f f e c t i v e m a s s . C o n t a m i n a t i o n f r o m f i n a l s t a t e s i n c l u d i n g a n e x t r a no has been investigated. This background was f o u n d to c o m e p r e d o m i n a n t l y f r o m t h e r e a c t i o n : K-p ~ Q-(1300) p Q-_~ (g~)-~o , c o n t r i b u t i n g l i t t l e b a c k g r o u n d to t h e K*(890) m a s s r e g i o n , b u t p o s i n g a s e r i o u s p r o b l e m in t h e K*(1420) r e g i o n . M i s s i n g m a s s c u t s w e r e i m p o s e d to r e d u c e t h i s c o n t a m i n a t i o n : M M 2 < 0.38 G e V 2 f o r e v e n t s b e s t f i t t i n g r e a c t i o n ( l b ) , a n d -0.1 < M M 2 < 0.1 G e V 2 f o r r e a c t i o n (2). T h e (Kv)- effective mass distribution from the sum of r e a c t i o n s (1) a n d (2) i s s h o w n in t h e u n s h a d e d h i s t o g r a m of fig. 2a. By e s t i m a t i n g t h e b a c k ground under the ~-o and ~T° peaks in the mlssing mass distributions of reactions (Ib) and (2) r e spectlvely, the cross section for the sum of r e actlons (I) and (2) can be determined. Then the cross section for reaction (2) (see table I) is determined by subtracting the reaction (1) cross section as determined from (In). K-p --* K*On. The main problem in the analysis of reactlon (3) is the contamination from "~ The K*(1429) branching fraction, (K*(1420)~ K~')/ (K*(1420)~total), l s t a k e n t o be 0 57 [3]

PHYSICS

Volume 38B, n u m b e r 4

t

.¼

500

Jr

20O

10C

200 +

100 ,o

5C dcTId t

pblC.c,y2 2O

20

10

10

21 F e b r u a r y 1972

e v e n t s w i t h a n e x t r a ;r o (the c r o s s s e c t i o n f o r t h e c h a n n e l ~+Tr-h w i t h u n o b s e r v e d h d e c a y i s m u c h s m a l l e r ) . C o n t a m i n a t i o n of t h i s t y p e i s e v i d e n t m the neutron missing mass distmbution which h a s a n e x c e s s of e v e n t s a b o v e t h e n e u t r o n m a s s . F u r t h e r , t h e K *o d e c a y a n g u l a r d i s t r i b u t i o n s f o r fitted events wtth m~ssing mass above and below t h e n e u t r o n m a s s a r e f o u n d to b e s i g n i f i c a n t l y d i f f e r e n t . T h e r e f o r e we h a v e u s e d only t h e l o w e r h a l f of t h e m i s s m g m a s s p e a k f o r r e a c t i o n (3) in t h e d e t e r m m a t m n of c r o s s s e c t i o n s ( t a b l e 1) a n d a n g u l a r d i s t r i b u h o n s . An i n v e s t i g a t i o n of t h e d i s t m b u t l o n of m i s s i n g m a s s f r o m t h e K - ~ + c o m b i n a t i o n in t h e r e a c t i o n

b) K-p ~ - K °~890)n

a) K-p ~ K'[890)P

LETTERS

K-p ~ K-~+~-p i n d i c a t e s t h a t b e t w e e n 10 a n d 1 5 ~ of t h e K ' ~ + n e v e n t s w i t h M M 2 < 0.88 G e V 2 c o u l d c o m e f r o m K-u+uOn. T h e K - ~ + e f f e c t i v e m a s s s p e c t r u m i s d i s p l a y e d m fig. 2b w h e r e E * o ( 8 9 0 ) a n d K * ° ( 1 4 2 0 ) peaks are ewdent with a comparatively small b a c k g r o u n d u n d e r t h e K*O(890). Angular distributions. The differentzai cross section for the reaction

5

2

2

0

-04

-08 0 t (GcV 2 )

-04

-08

Fig. 3. The differential c r o s s sections. The e r r o r s shown do not include the overall n o r m a h z a t i o n uncertainty given in table 1. a) K - p ~ K * - ( 8 9 0 ) p, b) K - p ~ K * ° ( 8 9 0 ) n.

K-p ~ K*-(890) p i s s h o w n m fig. 3a, w h e r e t h e K* e v e n t s a r e d e f i n e d b y 0.?6 < M(Ku) < 1.02 GeV. C o r r e c t i o n s have been made for scanning losses and for the l o s s of s t e e p l y d i p p i n g p r o t o n s . H o w e v e r , we cannot estimate, for the present data sample, t h e e x p e r i m e n t a l l o s s e s f o r e v e n t s w i t h ]t~ < 0.025 G e V 2. A 4 ± 4 ~ b c o r r e c t i o n h a s b e e n m a d e to t h e t o t a l c r o s s s e c t m n f o r t h i s r a n g e of t. T h e t u r n o v e r w h i c h i s p r e s e n t in t h e f o r ward direction has also been observed m other e x p e r i m e n t s a t l o w e r e n e r g i e s [ e . g . , 4] a n d i s n o t d u e to e x p e r i m e n t a l l o s s e s . A h t of t h e d i s t r i b u h o n to e x p (At) in t h e i n t e r n a l 0.1 < ] t l < 0.8 G e Y 2 y i e l d s A = 7.2 ± 0.4 G e V "2, i n d i c a t i n g c o n t i n u e d s h r i n k i n g of t h e f o r w a r d p e a k . T h e differential cross section for the reaction K - p -~ K*O(890) n,

t+++ 6 -o'2 -o'4

t GeV2 Fig. 4. The K* denmty m a t m x e l e m e n t s P00, P l - 1 and Re Pl0 as a function of momentum t r a n s f e r to the nucleon: a) K-p -*K*-(890) p, b) K-p ~K*°(890) n.

s h o w n in fig. 3b, s h o w s a f o r w a r d p e a k w i t h a n e x p o n e n t i a l s l o p e of 7.0 ± 1.1 G e V -2 f o r ] t l < 0.4 G e V 2. T h e d e c a y a n g u l a r d i s t r i b u t i o n s of K * ° ( 8 9 0 ) h a v e b e e n a n a l y s e d in t h e G o t t f r i e d - J a c k s o n f r a m e a s s u m i n g a p u r e 1 - s t a t e , d e f i n i n g t h e K* e v e n t s w i t h t h e m a s s c u t 0.76 < M(K~) < 1.02 GeV. It h a s b e e n c h e c k e d t h a t t h e v a l u e s o b tained for the density matrix elements for events f r o m r e a c t i o n s ( l b ) a n d (2) w e r e n o t s t r o n g l y d e p e n d e n t on t h e e x a c t s e p a r a t i o n b e t w e e n t h e s e two r e a c t i o n s , a n d t h a t t h e v a l u e s , a v e r a g e d 255

Volume 38B, n u m b e r 4

PHYSICS

over all t intervals, agreed with the sample from reaction (la). The density matrix elements P00, P l - 1 a n d Re P l 0 a r e p r e s e n t e d in h g . 4 m i n t e r v a l s of t f o r b o t h K * - a n d K *o p r o d u c t i o n . T h e h r s t r e a c t i o n i s s e e n to b e d o m i n a t e d b y n a t u r a l p a n t y e x c h a n g e ( P l l + P l - 1 ~ 0.9), w h i l e in t h e s e c o n d r e a c t i o n t h e u n n a t u r a l p a r i t y e x c h a n g e i s s t r o n g e r ( P l l + P l - 1 ~ 0.3). In t h e f o l l o w i n g l e t t e r we c o m p a r e o u r r e sults with those obtained at lower energy and m a k e a q u a h t a h v e i n t e r p r e t a t i o n of t h e e n e r g y d e p e n d e n c e of t h e s e r e a c t i o n s .

256

LETTERS

21 F e b r u a r y 1972

W e w i s h to e x p r e s s o u r t h a n k s to t h e m e m b e r s of t h e C E R N s t a f f w h o m a d e t h e t a k i n g of t h e d a t a p o s s i b l e , a n d to o u r d a t a p r o c e s s i n g a n d scannmg personnel.

References [1] W. G a i b r a i t h e t a l . , Phys. Rev. ]38 (1965) B913. [2] A. F i r e s t o n e e t a l . , Phys. L e t t e r s 36B (1971) 513; D. D. Carmony et al., Phys. Rev. L e t t e r s 27 (1971) 1160. [3] P a r t i c l e Data Group, April 1971. [4] M. Deutschmann et al., CERN/D. Ph. I I / P h y s . 71.24, Nucl. Phys., to be pubhshed.