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The observation in mica of tracks of charged particles from neutrino interactions
Volume 25B. number 4
THE
PHYSICS
OBSERVATION
IN FROM
LETTERS
4 September 1967
MICA OF TRACKS OF CHARGED NEUTRINO INTERACTIONS
PARTICLES
F. M. RUSSELL Rutherford
Evidence
has
been
Laboratory.
Chilton.
Berks.
1 England
found uhich suggests that charged particles \vhichmay have been produced by neutrino
interactions deep underground can leave observable the tracks are caused by muons
tracks
in mica.
Naturally occurring crystals of muscovite mica often exhibit an internal decoration composed of oxides of iron. This decoration is usually in the form of random spots and sets of straight lines lying in or near to the plane of easy cleavage (001). By far the great majority of such lines are orientated in directions which are related directly to the internal structure of the crystal. Nevertheless a small minority exist which are orientated essentially at random. A study of this minority class has led to the suggestion that they are caused by the passage of charged high energy particles through the crystal during a particular stage in the history of the crystal. The evidence upon which this suggestion is based is summarised here. First, the random nature of the distribution in the (001) plane of the lines in the minority class has been checked by x2 tests and indicates that the measurements were in accord with a random distribution. The results of measurements on two crystals are shown in fig. 1.
It is suggested
that the majority
of
T
t
,A _I-Li 0.1
1.0
Line
length
10
(cm)
Fig. 2.
0" F?e,ot,ve
*m-
f 30” OrlentCltlO”
I”
Fig. 1. 298
(001) plane
f
Secondly, the lines in the minority class are observed to lie within a range of angles of dip in the (001) plane, which is in sharp contrast to the lines in the majority class as these lie strictly in the plane of cleavage. This result has been established by direct measurement and by splitting along the cleavage planes. The measured range of angle of dip is about kO.3 milliradian for the
Volume 25B. n u m b e r 4
PHYSICS
LETTERS
4 S e p t e m b e r 1967
t ,o
tit ,[,.,l,ll I l~lll ~- i l i I i l l t
llij~t I I' O~
02
6
52
0'.4
o6
os
~.o
M 2 (GeV) 2 8'50
900
9~--~D M (IM eV)
1 (DO0 "
Fig. 1. Mass s p e c t r u m for y-p ~ p + M r e a c t i o n at 1.8 GeV/c. m a s s e s w i t h i s o s p i n z e r o a n d 1, r e s p e c t i v e l y . T h e s t u d y of t h e r e a c t i o n K - n ~ A ° X - [3, 4] s e e m s to i n d i c a t e t h a t t h e i s o s p i n of t h e X o i s zero, which favors the second hypothesis. N e v e r t h e l e s s , i t i s i n t e r e s t i n g to t r y to o b t a i n evidence for this resonance at an energy different f r o m t h o s e of [1] a n d [2]. A s e a r c h f o r t h e r e s o n a n c e 5- h a s b e e n m a d e a t t h e a c c e l e r a t o r S A TURNE in the reaction ~-p ~ p + 5- for an incident p i o n m o m e n t u m of 1800 M e V / c w h i c h i s 360 M e V / c a b o v e t h e t h r e s h o l d f o r t h e r e a c t i o n . By analogy with the excitation curves for the prod u c t i o n of t h e r e s o n a n c e s p, 7? a n d w in p i o n nucleon scattering, which are rapidly increasing a b o v e t h r e s h o l d , it i s r e a s o n a b l e to e x p e c t a 5production cross section sufficient for observation. The experimental method used consisted in looking at the missing mass for the proton. The a p p a r a t u s w a s c o m p o s e d of a s p a r k c h a m b e r spectrometer, w h i c h h a s b e e n d e s c r i b e d in a p r e v i o u s p a p e r [5]. T h e s p e c t r o m e t e r c o v e r e d a n a n g u l a r r e g i o n of 12 ° in t h e l a b o r a t o r y w i t h a n a v e r a g e a n g l e of 27 ° , w h i c h c o r r e s p o n d s to t h e l i m i t in r e c o i l a n g l e of a p r o t o n f o r a m i s s i n g m a s s of 960 M e V . T h e s e e x p e r i m e n t a l c o n d i t i o n s g a v e a v a r i a t i o n of c o s 0 b e t w e e n 0 a n d 0.9 f o r a m a s s r e g i o n e x t e n d i n g f r o m 850 to 1010 MeV, 0 being the angle between the incident a n d s c a t t e r e d p r o t o n s i n t h e c e n t e r of m a s s . In addition, those conditions gave the best resolut i o n . A ~ e r e n k o v c o u n t e r , p l a c e d a t t h e e x i t of t h e m a g n e t of t h e s p e c t r o m e t e r a l l o w e d t h e s e p a r a t i o n of p i o n s f r o m t h e s c a t t e r e d p r o t o n s up to a m o m e n t u m of 1500 M e V / c . The resolution in missing mass around 960 M e V i s + 10 MeV. T h i s r e s o l u t i o n w a s c a l -
Fig. 2. Spectrum of the M 2 (missing m a s s squared) for ?T-p ~ p + M reaction at 1.8 GeV/c. culated after having experimentally determined t h e d i s p e r s i o n s of v a r i o u s m e a s u r e d q u a n t i t i e s [6], t h a t i s , t h e i n c i d e n t m o m e n t u m , t h e p r o t o n momentum after scattering and the scattering angle. T h e s y s t e m a t i c e r r o r in t h e d e t e r m i n a t i o n of t h e m i s s i n g m a s s i s s m a l l e r t h a n 5 MeV. A M o n t e C a r l o m e t h o d w a s u s e d to d e t e r m i n e t h e s o l i d a n g l e of t h e a p p a r a t u s ( A n in t h e c . m . ) f o r e a c h m i s s i n g m a s s b a n d . It w a s t h e n p o s s i b l e to c a l c u l a t e t h e v a l u e s of d 2 c r / d M d ~ . In t h e m a s s r e g i o n 8 5 ~ - 1 0 1 0 MeV. the v a r i a t i o n of t h e m e a n v a l u e of d ~/dMd~ w i t h c o s ~ i s d i s p l a y e d i n fig. 1. T h i s s p e c t r u m d o e s not s h o w a n y s t r u c t u r e in t h e w h o l e m a s s b a n d c o n s i d e r e d . T h e n u m b e r of e v e n t s p e r 10 M e V b a n d b e t w e e n 900 M e V a n d 1000 M e V i s of t h e o r d e r of 1000. In the r e g i o n of t h e m a s s s p e c t r u m b e l o w 850 M e V , t h e a n g u l a r r e g i o n m e a s u r e d w a s s m a l l e r in the c e n t e r of m a s s (-0.1 < c o s 0 < 0.3), a n d c o r r e s p o n d e d to t ~ 1 ( G e V / c ) 2. T h e s p e c t r u m of t h e m i s s i n g m a s s s q u a r e d (fig. 2) s h o w s t h e e l a s t i c a n d t h e p p e a k s . T h e c u r v e i s a b e s t f i t to t h e d a t a o b t a i n e d w i t h a p o l y n o m i a l a n d a B r e i t W i g n e r of w i d t h a n d position determined by least squares. One obt a i n s Mp = ( 7 5 2 + 1 4 ) M e V a n d Fp = ( 1 0 0 + 3 0 ) M e V . The measured cross section for p- production, d~/dt i s c o m p a t i b l e w i t h t h a t o b t a i n e d b y A l l e n e t al. [7], a t 1.7 G e V / c . In t h e c a s e of t h e 5 - , t h e u p p e r l i m i t of t h e p r o d u c t i o n c r o s s s e c t i o n i s e q u a l to 3 I~b/(GeV/c) 2. T h e r e s u l t of t h i s e x p e r i m e n t i s i n d i s a g r e e m e n t w i t h t h a t of M a g l i c e t al. [1], u n l e s s one assumes an excitation curve very different from t h o s e g e n e r a l l y o b s e r v e d . In a d d i t i o n , i n t h e s t u d y of t h e r e a c t i o n ~ - p ~ p ~ - ~ o in a b u b b l e c h a m b e r [8], a m a s s s p e c t r u m of t h e d i p i o n ~ - ~ o h a s b e e n obtained, where a narrow peak appeared around 960 M e V . A s t h i s e x p e r i m e n t w a s d o n e a t a n i n c i d e n t m o m e n t u m c l o s e to o u r s (1.7 G e V / c ) a n d 301
Volume 25B. n u m b e r 4
PHYSICS
LETTERS
f o r a b a n d of m o m e n t u m t r a n s f e r to t h e p r o t o n w h i c h we o b s e r v e d , it i s c l e a r t h a t t h e i r c o n c l u s i o n s a n d t h e r e s u l t of o u r e x p e r i m e n t s a r e i n total disagreement.
References 1. M . N . F o c a c c i , W. Kienzle, B. Levrat, B . C . M a g l i d and M . M a r t i n , Phys. Rev. L e t t e r s 17 (1966) 890. 2. J. Oostens, P. Chavanon, M. Crozon and J. Tocqueville, Phys. L e t t e r s 22 (1966) 708.
~-K + ENHANCEMENT
IN
THE
4 S e p t e m b e r 1967
3. H.J. Martin J r . , R.R. Crittenden and L.S. Schroeder, Phys. L e t t e r s 22 (1966) 352. 4. R.Barloutaud et al., private communication. 5. M . B a n n e r , J . F . D e t o e u f , M . L . F a y o u x , J . L . H a m e l , J. Movchet, L. van Rossum, J. Cheze, J. T e i g e r and J . Z s e m b e r y , Phys. L e t t e r s 21 (1966) 582. 6. J . L . H a m e l , Th~se 3e Cycle, Facult~ des Sciences d'Orsay, 1967. 7. D.D.Allen, G. P. F i s h e r , G.Godden, J . B . Kopelman, L. M a r s h a l l and R. Sears, Phys. Rev. L e t t e r s 17 (1966) 53. 8. D.D.Allen, G . P . F i s h e r , G.Godden, L . M a r s h a l l and R . S e a r s , Phys. L e t t e r s 22 (1966) 543.
REACTION
~-p
P. J . W E I S B A C H , C. G. HOWARD, T. R. P A L F R E Y J r .
~
F.-K+~
o :~
a n d R. J . SAHNI
Department of Physics, Purdue University, Lafayette, Indiana, USA Received 2 August 1967 The reaction 7r-p --~ F.-K+~ ° has been studied at incident pion laboratory momentum of 5.0 GeV/c. Evidence is p r e s e n t e d that this reaction proceeds through excitation and subsequent Z-K + decay of the N*(1570) isobar.
At h i g h e n e r g i e s s t r a n g e p a r t i c l e p r o d u c t i o n in 7r-p i n t e r a c t i o n s i s d o m i n a t e d b y p e r i p h e r a l K a n d K* e x c h a n g e , n e i t h e r of w h i c h i s a p o s s i b l e mechanism for the reaction ~-p ~ Z-K+~ ° .
(1)
P r e v i o u s e x p e r i m e n t s [e. g. 1] at l o w e r e n e r g i e s s h o w a m a r k e d d e c r e a s e of k n o w n K* a n d Y* p r o d u c t i o n in r e a c t i o n (1) w i t h i n c r e a s i n g e n e r g y . T h i s l e t t e r p r e s e n t s e v i d e n c e t h a t r e a c t i o n (1) a t 5.0 G e V / c p r o c e e d s p e r i p h e r a l l y a s ~ - p ~ N*°Tr °
(2)
w i t h N *o b r a n c h i n g to Z - K +, a n d a t t e m p t s a n i n t e r p r e t a t i o n in t e r m s of the N*(1570) S l l r e s o n a n c e , b e l o w Z K t h r e s h o l d [2]. T h e p o s s i b l e a s s i g n m e n t of t h i s r e s o n a n c e to a n SU(3) b a r y o n o c tet is also discussed. The experimental results reported here are o b t a i n e d f r o m h a l f of a 150 000 p i c t u r e e x p o s u r e to a 5.0 G e V / c ~ - b e a m in t h e 72 i n c h L R L A l v a r e z h y d r o g e n b u b b l e c h a m b e r "~. A s a m p l e of 27 e v e n t s w a s u n i q u e l y i d e n t i f i e d a s r e a c t i o n (1). An a d d i t i o n a l s a m p l e of 43 e v e n t s w a s f o u n d to s a t i s fy one o r m o r e a d d i t i o n a l h y p o t h e s e s . M o s t of t h e l a t t e r w e r e a m b i g u o u s w i t h t h e f i n a l s t a t e ~ - K ° n +. 302
Fig. 1 s h o w s a n M 2 ( ~ - ~ °) v e r s u s M 2 ( K + g °) Dalitz plot and its projections for the unambiguous events. As one would anticipate by extrapolat i o n of low e n e r g y d a t a , t h e r e i s no e v i d e n c e f o r K* o r Y* f o r m a t i o n . T h e C h e w - L o w p l o t , fig. 2(a), shows a dramatic low-mass B-K + enhancement: t h e c o n c e n t r a t i o n of e v e n t s c o r r e s p o n d i n g to M ( E - K +) ~ < 2 . 2 G e V a n d A 2~< 0.5 ( G e V / c ) 2. T h i s s a m p l e r e p r e s e n t s 16 of t h e t o t a l 27 u n a m b i g u o u s e v e n t s , g i v i n g a c r o s s s e c t i o n of 5.5 ~ b a r n . T h e E - K + m a s s d i s t r i b u t i o n , fig. 2(b), d e m o n s t r a t e s t h a t t h e d a t a a r e not in a g r e e m e n t w i t h o r d i n a r y phase space. E v e n w i t h t h e i n c l u s i o n of a m b i g u o u s e v e n t s , t h e l o w - m a s s , l o w - A2 e n h a n c e m e n t r e m a i n s . A n a l y s i s of t h e e v e n t s on t h e k i n e m a t i c h y p o t h e s i s ~ - p ~ ~ - K + + ( m i s s i n g m a s s ) r e v e a l s t h a t ~15% of t h e e v e n t s a r e c o n s i s t e n t w i t h m o r e t h a n one m i s s i n g ~o. H o w e v e r , in t h e l o w - m a s s , l o w - A 2 r e g i o n t h e t r a c k s s e e n a r e of low m o m e n t u m a n d t h u s w e l l m e a s u r e d , s o t h e f i t t i n g to r e a c t i o n (1) d o e s not b i a s t h e E - K + d i s t r i b u t i o n s s i g n i f i c a n t l y . Work supported in part by the U.S. Atomic Energy Commission. P a r t of a collaboration between the University of Illinois and Purdue University. Data on A o and ~ o final states include events from the Illinois group of C. Bridges and T. O'Halloran.
THE
PHYSICS
OBSERVATION
IN FROM
LETTERS
4 September 1967
MICA OF TRACKS OF CHARGED NEUTRINO INTERACTIONS
PARTICLES
F. M. RUSSELL Rutherford
Evidence
has
been
Laboratory.
Chilton.
Berks.
1 England
found uhich suggests that charged particles \vhichmay have been produced by neutrino
interactions deep underground can leave observable the tracks are caused by muons
tracks
in mica.
Naturally occurring crystals of muscovite mica often exhibit an internal decoration composed of oxides of iron. This decoration is usually in the form of random spots and sets of straight lines lying in or near to the plane of easy cleavage (001). By far the great majority of such lines are orientated in directions which are related directly to the internal structure of the crystal. Nevertheless a small minority exist which are orientated essentially at random. A study of this minority class has led to the suggestion that they are caused by the passage of charged high energy particles through the crystal during a particular stage in the history of the crystal. The evidence upon which this suggestion is based is summarised here. First, the random nature of the distribution in the (001) plane of the lines in the minority class has been checked by x2 tests and indicates that the measurements were in accord with a random distribution. The results of measurements on two crystals are shown in fig. 1.
It is suggested
that the majority
of
T
t
,A _I-Li 0.1
1.0
Line
length
10
(cm)
Fig. 2.
0" F?e,ot,ve
*m-
f 30” OrlentCltlO”
I”
Fig. 1. 298
(001) plane
f
Secondly, the lines in the minority class are observed to lie within a range of angles of dip in the (001) plane, which is in sharp contrast to the lines in the majority class as these lie strictly in the plane of cleavage. This result has been established by direct measurement and by splitting along the cleavage planes. The measured range of angle of dip is about kO.3 milliradian for the
Volume 25B. n u m b e r 4
PHYSICS
LETTERS
4 S e p t e m b e r 1967
t ,o
tit ,[,.,l,ll I l~lll ~- i l i I i l l t
llij~t I I' O~
02
6
52
0'.4
o6
os
~.o
M 2 (GeV) 2 8'50
900
9~--~D M (IM eV)
1 (DO0 "
Fig. 1. Mass s p e c t r u m for y-p ~ p + M r e a c t i o n at 1.8 GeV/c. m a s s e s w i t h i s o s p i n z e r o a n d 1, r e s p e c t i v e l y . T h e s t u d y of t h e r e a c t i o n K - n ~ A ° X - [3, 4] s e e m s to i n d i c a t e t h a t t h e i s o s p i n of t h e X o i s zero, which favors the second hypothesis. N e v e r t h e l e s s , i t i s i n t e r e s t i n g to t r y to o b t a i n evidence for this resonance at an energy different f r o m t h o s e of [1] a n d [2]. A s e a r c h f o r t h e r e s o n a n c e 5- h a s b e e n m a d e a t t h e a c c e l e r a t o r S A TURNE in the reaction ~-p ~ p + 5- for an incident p i o n m o m e n t u m of 1800 M e V / c w h i c h i s 360 M e V / c a b o v e t h e t h r e s h o l d f o r t h e r e a c t i o n . By analogy with the excitation curves for the prod u c t i o n of t h e r e s o n a n c e s p, 7? a n d w in p i o n nucleon scattering, which are rapidly increasing a b o v e t h r e s h o l d , it i s r e a s o n a b l e to e x p e c t a 5production cross section sufficient for observation. The experimental method used consisted in looking at the missing mass for the proton. The a p p a r a t u s w a s c o m p o s e d of a s p a r k c h a m b e r spectrometer, w h i c h h a s b e e n d e s c r i b e d in a p r e v i o u s p a p e r [5]. T h e s p e c t r o m e t e r c o v e r e d a n a n g u l a r r e g i o n of 12 ° in t h e l a b o r a t o r y w i t h a n a v e r a g e a n g l e of 27 ° , w h i c h c o r r e s p o n d s to t h e l i m i t in r e c o i l a n g l e of a p r o t o n f o r a m i s s i n g m a s s of 960 M e V . T h e s e e x p e r i m e n t a l c o n d i t i o n s g a v e a v a r i a t i o n of c o s 0 b e t w e e n 0 a n d 0.9 f o r a m a s s r e g i o n e x t e n d i n g f r o m 850 to 1010 MeV, 0 being the angle between the incident a n d s c a t t e r e d p r o t o n s i n t h e c e n t e r of m a s s . In addition, those conditions gave the best resolut i o n . A ~ e r e n k o v c o u n t e r , p l a c e d a t t h e e x i t of t h e m a g n e t of t h e s p e c t r o m e t e r a l l o w e d t h e s e p a r a t i o n of p i o n s f r o m t h e s c a t t e r e d p r o t o n s up to a m o m e n t u m of 1500 M e V / c . The resolution in missing mass around 960 M e V i s + 10 MeV. T h i s r e s o l u t i o n w a s c a l -
Fig. 2. Spectrum of the M 2 (missing m a s s squared) for ?T-p ~ p + M reaction at 1.8 GeV/c. culated after having experimentally determined t h e d i s p e r s i o n s of v a r i o u s m e a s u r e d q u a n t i t i e s [6], t h a t i s , t h e i n c i d e n t m o m e n t u m , t h e p r o t o n momentum after scattering and the scattering angle. T h e s y s t e m a t i c e r r o r in t h e d e t e r m i n a t i o n of t h e m i s s i n g m a s s i s s m a l l e r t h a n 5 MeV. A M o n t e C a r l o m e t h o d w a s u s e d to d e t e r m i n e t h e s o l i d a n g l e of t h e a p p a r a t u s ( A n in t h e c . m . ) f o r e a c h m i s s i n g m a s s b a n d . It w a s t h e n p o s s i b l e to c a l c u l a t e t h e v a l u e s of d 2 c r / d M d ~ . In t h e m a s s r e g i o n 8 5 ~ - 1 0 1 0 MeV. the v a r i a t i o n of t h e m e a n v a l u e of d ~/dMd~ w i t h c o s ~ i s d i s p l a y e d i n fig. 1. T h i s s p e c t r u m d o e s not s h o w a n y s t r u c t u r e in t h e w h o l e m a s s b a n d c o n s i d e r e d . T h e n u m b e r of e v e n t s p e r 10 M e V b a n d b e t w e e n 900 M e V a n d 1000 M e V i s of t h e o r d e r of 1000. In the r e g i o n of t h e m a s s s p e c t r u m b e l o w 850 M e V , t h e a n g u l a r r e g i o n m e a s u r e d w a s s m a l l e r in the c e n t e r of m a s s (-0.1 < c o s 0 < 0.3), a n d c o r r e s p o n d e d to t ~ 1 ( G e V / c ) 2. T h e s p e c t r u m of t h e m i s s i n g m a s s s q u a r e d (fig. 2) s h o w s t h e e l a s t i c a n d t h e p p e a k s . T h e c u r v e i s a b e s t f i t to t h e d a t a o b t a i n e d w i t h a p o l y n o m i a l a n d a B r e i t W i g n e r of w i d t h a n d position determined by least squares. One obt a i n s Mp = ( 7 5 2 + 1 4 ) M e V a n d Fp = ( 1 0 0 + 3 0 ) M e V . The measured cross section for p- production, d~/dt i s c o m p a t i b l e w i t h t h a t o b t a i n e d b y A l l e n e t al. [7], a t 1.7 G e V / c . In t h e c a s e of t h e 5 - , t h e u p p e r l i m i t of t h e p r o d u c t i o n c r o s s s e c t i o n i s e q u a l to 3 I~b/(GeV/c) 2. T h e r e s u l t of t h i s e x p e r i m e n t i s i n d i s a g r e e m e n t w i t h t h a t of M a g l i c e t al. [1], u n l e s s one assumes an excitation curve very different from t h o s e g e n e r a l l y o b s e r v e d . In a d d i t i o n , i n t h e s t u d y of t h e r e a c t i o n ~ - p ~ p ~ - ~ o in a b u b b l e c h a m b e r [8], a m a s s s p e c t r u m of t h e d i p i o n ~ - ~ o h a s b e e n obtained, where a narrow peak appeared around 960 M e V . A s t h i s e x p e r i m e n t w a s d o n e a t a n i n c i d e n t m o m e n t u m c l o s e to o u r s (1.7 G e V / c ) a n d 301
Volume 25B. n u m b e r 4
PHYSICS
LETTERS
f o r a b a n d of m o m e n t u m t r a n s f e r to t h e p r o t o n w h i c h we o b s e r v e d , it i s c l e a r t h a t t h e i r c o n c l u s i o n s a n d t h e r e s u l t of o u r e x p e r i m e n t s a r e i n total disagreement.
References 1. M . N . F o c a c c i , W. Kienzle, B. Levrat, B . C . M a g l i d and M . M a r t i n , Phys. Rev. L e t t e r s 17 (1966) 890. 2. J. Oostens, P. Chavanon, M. Crozon and J. Tocqueville, Phys. L e t t e r s 22 (1966) 708.
~-K + ENHANCEMENT
IN
THE
4 S e p t e m b e r 1967
3. H.J. Martin J r . , R.R. Crittenden and L.S. Schroeder, Phys. L e t t e r s 22 (1966) 352. 4. R.Barloutaud et al., private communication. 5. M . B a n n e r , J . F . D e t o e u f , M . L . F a y o u x , J . L . H a m e l , J. Movchet, L. van Rossum, J. Cheze, J. T e i g e r and J . Z s e m b e r y , Phys. L e t t e r s 21 (1966) 582. 6. J . L . H a m e l , Th~se 3e Cycle, Facult~ des Sciences d'Orsay, 1967. 7. D.D.Allen, G. P. F i s h e r , G.Godden, J . B . Kopelman, L. M a r s h a l l and R. Sears, Phys. Rev. L e t t e r s 17 (1966) 53. 8. D.D.Allen, G . P . F i s h e r , G.Godden, L . M a r s h a l l and R . S e a r s , Phys. L e t t e r s 22 (1966) 543.
REACTION
~-p
P. J . W E I S B A C H , C. G. HOWARD, T. R. P A L F R E Y J r .
~
F.-K+~
o :~
a n d R. J . SAHNI
Department of Physics, Purdue University, Lafayette, Indiana, USA Received 2 August 1967 The reaction 7r-p --~ F.-K+~ ° has been studied at incident pion laboratory momentum of 5.0 GeV/c. Evidence is p r e s e n t e d that this reaction proceeds through excitation and subsequent Z-K + decay of the N*(1570) isobar.
At h i g h e n e r g i e s s t r a n g e p a r t i c l e p r o d u c t i o n in 7r-p i n t e r a c t i o n s i s d o m i n a t e d b y p e r i p h e r a l K a n d K* e x c h a n g e , n e i t h e r of w h i c h i s a p o s s i b l e mechanism for the reaction ~-p ~ Z-K+~ ° .
(1)
P r e v i o u s e x p e r i m e n t s [e. g. 1] at l o w e r e n e r g i e s s h o w a m a r k e d d e c r e a s e of k n o w n K* a n d Y* p r o d u c t i o n in r e a c t i o n (1) w i t h i n c r e a s i n g e n e r g y . T h i s l e t t e r p r e s e n t s e v i d e n c e t h a t r e a c t i o n (1) a t 5.0 G e V / c p r o c e e d s p e r i p h e r a l l y a s ~ - p ~ N*°Tr °
(2)
w i t h N *o b r a n c h i n g to Z - K +, a n d a t t e m p t s a n i n t e r p r e t a t i o n in t e r m s of the N*(1570) S l l r e s o n a n c e , b e l o w Z K t h r e s h o l d [2]. T h e p o s s i b l e a s s i g n m e n t of t h i s r e s o n a n c e to a n SU(3) b a r y o n o c tet is also discussed. The experimental results reported here are o b t a i n e d f r o m h a l f of a 150 000 p i c t u r e e x p o s u r e to a 5.0 G e V / c ~ - b e a m in t h e 72 i n c h L R L A l v a r e z h y d r o g e n b u b b l e c h a m b e r "~. A s a m p l e of 27 e v e n t s w a s u n i q u e l y i d e n t i f i e d a s r e a c t i o n (1). An a d d i t i o n a l s a m p l e of 43 e v e n t s w a s f o u n d to s a t i s fy one o r m o r e a d d i t i o n a l h y p o t h e s e s . M o s t of t h e l a t t e r w e r e a m b i g u o u s w i t h t h e f i n a l s t a t e ~ - K ° n +. 302
Fig. 1 s h o w s a n M 2 ( ~ - ~ °) v e r s u s M 2 ( K + g °) Dalitz plot and its projections for the unambiguous events. As one would anticipate by extrapolat i o n of low e n e r g y d a t a , t h e r e i s no e v i d e n c e f o r K* o r Y* f o r m a t i o n . T h e C h e w - L o w p l o t , fig. 2(a), shows a dramatic low-mass B-K + enhancement: t h e c o n c e n t r a t i o n of e v e n t s c o r r e s p o n d i n g to M ( E - K +) ~ < 2 . 2 G e V a n d A 2~< 0.5 ( G e V / c ) 2. T h i s s a m p l e r e p r e s e n t s 16 of t h e t o t a l 27 u n a m b i g u o u s e v e n t s , g i v i n g a c r o s s s e c t i o n of 5.5 ~ b a r n . T h e E - K + m a s s d i s t r i b u t i o n , fig. 2(b), d e m o n s t r a t e s t h a t t h e d a t a a r e not in a g r e e m e n t w i t h o r d i n a r y phase space. E v e n w i t h t h e i n c l u s i o n of a m b i g u o u s e v e n t s , t h e l o w - m a s s , l o w - A2 e n h a n c e m e n t r e m a i n s . A n a l y s i s of t h e e v e n t s on t h e k i n e m a t i c h y p o t h e s i s ~ - p ~ ~ - K + + ( m i s s i n g m a s s ) r e v e a l s t h a t ~15% of t h e e v e n t s a r e c o n s i s t e n t w i t h m o r e t h a n one m i s s i n g ~o. H o w e v e r , in t h e l o w - m a s s , l o w - A 2 r e g i o n t h e t r a c k s s e e n a r e of low m o m e n t u m a n d t h u s w e l l m e a s u r e d , s o t h e f i t t i n g to r e a c t i o n (1) d o e s not b i a s t h e E - K + d i s t r i b u t i o n s s i g n i f i c a n t l y . Work supported in part by the U.S. Atomic Energy Commission. P a r t of a collaboration between the University of Illinois and Purdue University. Data on A o and ~ o final states include events from the Illinois group of C. Bridges and T. O'Halloran.