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Submitted on 1 Jan 1982
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OBSERVATION OF THE RADIATIVE DECAY J/Ψ → γ η π π
C. Newman-Holmes
To cite this version:
C. Newman-Holmes. OBSERVATION OF THE RADIATIVE DECAY J/Ψ → γ η π π. Journal de
Physique Colloques, 1982, 43 (C3), pp.C3-82-C3-85. �10.1051/jphyscol:1982317�. �jpa-00221870�
D e p a r t m e n t o f P h y s i c s , P r i n c e t o n U n i v e r s i t y , P r i n c e t o n , New J e r s e y 0 8 5 4 4 , U. S.A.
R e c e n t l y a r e s o n a n c e w i t h m a s s 1 4 4 0 MeV h a s b e e n s e e n i n t h e KKn m a s s s p e c t r u m f r o m t h e r a d i a t i v e d e c a y J / $ + YKKv [ 1 , 2 ] . P a r -
t i a l w a v e a n d s p i n p a r i t y a n a l y s e s p e r f o r m e d b y t h e C r y s t a l B a l l c o l l a b o r a t i o n [ 2 ] i n d i c a t e d t h a t t h e s t a t e w a s a p s e u d o s c a l a r w h i c h d e c a y e d p r e d o m i n a n t l y t o 6 n w i t h t h e 6 d e c a y i n g t o
K K .
T h i s s t a t e h a s b e e n n a m e d ~ ( 1 4 4 0 ) . T h e 6 ( 9 8 0 ) a l s o d e c a y s t o n n a n d t h eb r a n c h i n g r a t i o f o r t h i s c h a n n e l m i g h t b e e x p e c t e d t o b e l a r g e r t h a n t h e b r a n c h i n g r a t i o t o
KE
b e c a u s e t h e 6 m a s s i s b e l o wKE
t h r e s h o l d . One e x p e r i m e n t [ 3 ] f i n d s : B R ( 6 + l l n ) / ~ ~ ( 6 +KP)
= 1 . 4 f 0 . 6 . T h u s we e x p e c t t h e l ( 1 4 4 0 ) t o a p p e a r i n t h e n r n m a s s s p e c t r u m f r o m t h e p r o c e s s J / $ + y n n n . I w i l l p r e s e n t r e s u l t s f r o m a s t u d y o f t h i s p r o c e s s b y t h e C r y s t a l B a l l c o l l a b o r a t i o n 1 4 1 .T h e d a t a a r e f r o m a s a m p l e o f 2 . 2 m i l l i o n J / $ ' s p r o d u c e d i n e + e - i n t e r a c t i o n s a t t h e SPEAR s t o r a g e r i n g . T h e C r y s t a l B a l l d e t e c t o r p r i m a r i l y c o n s i s t s o f a s e g m e n t e d s p h e r i c a l s h e l l o f N ~ I ( T L ) c r y s t a l s c o v e r i n g 9 3 % o f t h e f u l l s o l i d a n l e . T h e e n e r g y r e s o l u t i o n f o r p h o t o n s i s g i v e n b y o E / E = 0 . 0 2 6 / E 1 8 4 ( E i n G ~ v ) . T h e p h o t o n a n g u l a r r e s o l u t i o n i s 2 5 - 4 0 m r a d , d e p e n d i n g o n e n e r g y . An i n n e r d e t e c t o r , c o n s i s t i n g o f m a g n e t o s t r i c t i v e s p a r k c h a m b e r s a n d p r o p o r t i o n a l w i r e c h a m b e r s , w a s u s e d t o i d e n t i f y c h a r g e d p a r t i - c l e s a n d m e a s u r e t h e i r d i r e c t i o n s . D e t a i l s o f t h e d e t e c t o r p e r f o r - m a n c e a n d e v e n t s e l e c t i o n p r o c e d u r e s h a v e b e e n p r e s e n t e d e l s e - w h e r e [ 5 ] .
F o r t h i s a n a l y s i s , h a d r o n i c d e c a y s o f t h e J / $ w e r e s e l e c t e d w h i c h c o n t a i n e d t h r e e p h o t o n s a n d t w o c h a r g e d p a r t i c l e s o r s e v e n p h o t o n s a n d n o c h a r g e d p a r t i c l e s . A k i n e m a t i c f i t w a s p e r f o r m e d o n e v e n t s w i t h 3 p h o t o n s a n d 2 c h a r g e d p a r t i c l e s , a s s u m i n g t h e y c a m e f r o m J / $ + y q n + n - w i t h t h e TI d e c a y i n g t o y y 1 6 1 . T h e s e v e n - p h o t o n e v e n t s w e r e f i t t o t h e h y p o t h e s e s J / $ + y n n 0 n 0 a s s u m i n g t h e
n
a n d b o t h n o ' s d e c a y e d t o t w o p h o t o n s . F i g u r e 1 s h o w s t h e n n s m a s s d i s t r i b u t i o n f o r e v e n t s w h i c h f i t t h e y n n n h y p o t h e s i s w i t h c o n f i - d e n c e l e v e l g r e a t e r t h a n 1 % . B o t h F i g u r e s l a a n d l b s h o w a n a r r o w p e a k a t 9 6 0 MeV c o r r e s p o n d i n g t o t h e d e c a y J / $ + Y V ' ,n '
+ n u n . I n a d d i t i o n , b o t h p l o t s s h o w a b r o a d e n h a n c e m e n t a t r o u g h l y 1 7 0 0 MeV.T h e d a s h e d c u r v e i n F i g u r e l a s h o w s t h e n n + n - s p e c t r u m e x p e c t e d f o r J / $ + y n n + n - L o r e n t z i n v a r i a n t p h a s e s p a c e e v e n t s . T h e e n h a n c e m e n t s e e n i n b o t h n n u s p e c t r a i s u n l i k e t h e p h a s e s p a c e d i s t r i b u t i o n . T h e r e i s n o e x p l i c i t e v i d e n c e f o r t h e l ( 1 4 4 0 ) t h o u g h i t c o u l d b e c o n t r i b u t i n g t o t h e b r o a d e n h a n c e m e n t . I w i l l p r e s e n t a n u p p e r l i m i t f o r t h e d e c a y J / $ + y 1, 1 + n n n l a t e r i n t h i s t a l k . F i r s t I w i l l d i s c u s s t h e new e n h a n c e m e n t i n m o r e d e t a i l .
S e v e r a l t e s t s h a v e b e e n p e r f o r m e d t o i n v e s t i g a t e t h e e n h a n c e - m e n t . To s t u d y t h e s t r e n g t h o f t h e
n
s i g n a l i n t h e d a t a , t h en
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982317
C. Newman-Holmes
F i g u r e 1
15 "
f
-
F i g u r e 1: qns s p e c t r u m f o r J/$ + yqss e v e n t s . F i g u r e l a i s nn n mass and F i g u r e l b i s rlnOnO m a s s . The dashed c u r v e i n F i g u r e l a shows rla+n- mass s p e c t r u m e x p e c t e d from L o r e n t z i n v a r i a n t phase s p a c e .
F i g u r e 2
-
1 502
c3- F i g u r e 2 : yy mass f o r e v e n t s
2
100which f i t t h e h y p o t h e s i s J/$ -t
4j
yyyn+s-.
+
ZW
>
W 50
0
0 0.5 1 .O 1.5
M,, (GeV)
c o n s t r a i n t w a s r e m o v e d f r o m t h e f i t . E v e n t s w i t h t h r e e p h o t o n s a n d t w o c h a r g e d p a r t i c l e s w e r e f i t t o t h e h y p o t h e s i s J / $ + ~ ~ ~ n + n - . F i g u r e 2 s h o w s t h e y y m a s s f o r e v e n t s w h i c h f i t w i t h c o n f i d e n c e l e v e l g r e a t e r t h a n 1 % . A l l y y c o m b i n a t i o n s a r e i n c l u d e d s o t h e r e a r e t h r e e e n t r i e s p e r e v e n t . C l e a r s i g n a l s a r e s e e n f o r t h e n o a n d
n
w i t h v e r y l i t t l e b a c k g r o u n d . I n a d d i t i o n we f i n d t h a t t h e b r o a d e n h a n c e m e n t i n n n n i s c o r r e l a t e d o n l y w i t h yY m a s s e s i n t h en
p e a k .T h e r e i s a l s o t h e p o s s i b i l i t y t h a t t h e e n h a n c e m e n t c o m e s f r o m s o m e o t h e r J / $ d e c a y , p e r h a p s w i t h o n e o r m o r e p a r t i c l e s m i s s i n g . Known d e c a y s o f t h e J / $ c a n n o t b e r e s p o n s i b l e b e c a u s e t h e sum o f k n o w n J / $ d e c a y s w h i c h c o n t a i n a n i s n o t l a r g e e n o u g h t o a c c o u n t f o r t h e s i g n a l . F o r e x a m p l e , t h e d e c a y J / $ + + a + % - ,
+
+nY, n
+y y w o u l d p r o d u c e o n l y a b o u t 2 5 e v e n t s i n o u r s a m p l e o f 2 . 2 m i l l i o n J . W i t h a d e t e c t i o n e f f i c i e n c y o f 2 0 % we w o u l d e x p e c t t o s e e 5 e v e n t s . T h e n u m b e r o f e v e n t s i n t h e b r o a d e n h a n c e m e n t i s a b o u t 1 0 0 t i m e s l a r g e r . S i m i l a r l y , p r o c e s s e s s u c h a s J / $ + y B , 8 + n n w i t h o n e
n
d e c a y i n g t o t h r e e p i o n s , ( o n e o f w h i c h i s n o t d e t e c t e d ) , c a n n o t c o m e c l o s e t o a c c o u n t i n g f o r a n e n h a n c e m e n t a s l a r g e a s we s e e .T h e e n h a n c e m e n t i s a p p a r e n t l y n o t a s s o c i a t e d w i t h a 6 , o r a n y o t h e r r e s o n a n c e s i n e i t h e r n n o r n n . D a l i t z p l o t s h a v e b e e n m a d e f o r J / $ + y n n + n - e v e n t s w i t h Mnn+,- n e a r t h e c e n t e r o f t h e p e a k . T h e d e c a y 6 ( 9 8 O ) + nn w o u l d p r o d u c e b a n d s n e a r M~~~ = 1 . 0 G e V 2 . No s u c h b a n d s a r e s e e n .
I s u g g e s t t h r e e p o s s i b l e i n t e r p r e t a t i o n s f o r t h i s new e n h a n c - e m e n t . F i r s t , t h e n n n m a s s d i s t r i b u t i o n f o r e v e n t s w h i c h c o n t a i n a p r o m p t y may b e q u i t e d i f f e r e n t f r o m L o r e n t z i n v a r i a n t p h a s e
s p a c e . T h e n t h e e n h a n c e m e n t c o u l d a r i s e f r o m t h e ( n o n r e s o n a n t ) d e c a y o f t h e J / $ t o a p h o t o n p l u s t w o g l u o n s : J / $ + y g g . S e c o n d l y , t h e e n h a n c e m e n t c o u l d b e a s i n g l e r e s o n a n c e . A t h i r d p o s s i b i l i t y i s t h a t i t i s a g r o u p o f r e s o n a n c e s .
T h e d a t a may b e f i t w i t h a s i n g l e B r e i t - W i g n e r l i n e s h a p e . F o r t h e f i t , t h e n r + n - a n d n n O n O m a s s s p e c t r a a r e f i t s i m u l t a n - e o u s l y w i t h t h e m a s s a n d w i d t h p a r a m e t e r s c o n s t r a i n e d t o b e t h e s a m e f o r b o t h c h a n n e l s . A c o n s t a n t b a c k g r o u n d w a s a s s u m e d f o r t h e n n O n O c h a n n e l . F o r n n + n - , we u s e d a b a c k g r o u n d d e t e r m i n e d b y f i t t i n g t h e y y n + n - m a s s s p e c t r u m f o r e v e n t s w i t h a Y Y m a s s c o m b i n - a t i o n i n t h e
n
s i d e b a n d s . ( 3 2 0<
M y y<
4 7 0 MeV o r 6 1 0<
M y y < 7 6 0 MeV).
T h e f i t h a s a
x2
o f 6 6 f o r 6 9 d e g r e e s o f f r e e d o m . We f i n d : M 1 7 1 0 f 4 5 MeV a n dr
= 5 3 0 f 1 1 0 MeV w h e r e t h e e r r o r s i n c l u d e e s t i m a t e s o f t h e s y s t e m a t i c u n c e r t a i n t y . T h e d e t e c t i o n e f f i c i e n c y w a s d e t e r m i n e d b y a M o n t e C a r l o c a l c u l a t i o n t o b e 1 8 % ( 6 . 6 % ) f o r J / $ + y n n + n - ( n n O n O ) ,n
+ y y f o r M n e a r 1 7 0 0 Mev. U s i n g t h e n u m b e r o f e v e n t s i n t h e p e a k , a s 2 z ; e r m i n e d b y t h e f i t , o n e o b t a i n s t h e b r a n c h i n g r a t i o s :w h e r e t h e f i r s t e r r o r i s s t a t i s t i c a l a n d t h e s e c o n d s y s t e m a t i c . T h e s e b r a n c h i n g r a t i o s a r e c o m p a r a b l e t o t h o s e o f t h e l a r g e s t k n o w n r a d i a t i v e d e c a y s o f t h e J/$.
T h e r e i s n o e v i d e n c e f o r l ( 1 4 4 0 ) i n t h e n n O n O m a s s s p e c t r u m . T h e n r + n - m a s s s p e c t r u m h a s a s l i g h t s h o u l d e r i n t h e I r e g i o n . T o
C. Newman-Holmes
obtain an upper limit for the decay of the 1 to nnn, the nnn mass spectra have been refit with an additional term for the t(1440).
The mass and width of the I were fixed but the mass and width of the Breit-Wigner line shape used to describe the new enhancement were allowed to vary. T h e result is
BR(J/$ + y ~ ) ( I + nnn )
<
2 x (90% confidence level).For comparison, note that [1,2]
BR(J/+ + y I ) ( I + KKn) = 4 x
In conclusion, we have observed the radiative decays J / $ +
ynn'n- and J/$ + Y n n0n0. We find
BR(J/Q + ") ( I +
" ' ) <
0.5 (90% confidence level) BR(J/$ + YI) ( 1 + KRn)There is a broad enhancement near 1700 MeV in the nnn m a s s spectrum which is produced with a substantial branching ratio.
Its origin is uncertain.
References
*Work supported in part by the Department of Energy, c o n t r a c t s DE-AC02-76ER03072 (Princeton) and DE-AC03-76SF00515 (SLAC).
I . SCHARRE, D.L. et al., Phys. Lett.
E,
(1980) 329.2. EDWARDS, C. et al., Phys. Rev. Lett.
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(1982) 259 3. STANTON, N.R. et al., Phys. Rev. Lett.42,
(1979) 346.4. The Crystal Ball collaboration includes: C. Edwards, R.
Partridge, C. P e c k , F. Porter (California Institute of Technology); D. Antreasyan, Y. F. G u , 3. Irion, W. Kollmann, M. Richardson, K. Strauch, A. Weinstein (Harvard University);
D. Aschman, T. Burnett (visitor), M. Cavalli-Sforza, D.
Coyne, C. Newman-Holmes, H. Sadrozinski (Princeton
University); E. Bloom, F. Bulos, R. Chestnut, J. G a i s e r , G.
G o d f r e y , C. Kiesling, J. L e f f l e r , W. Lockman, S. L o w e , M.
Oreglia, D. Scharre, K. Wacker (Stanford Linear Accelerator Center); D. Gelphman, R. Hofstadter, R. Horisberger, I.
Kirkbride, H. Kolanoski, K. Ksnigsmann, R. Lee, A. Liberman, J. O 1 R e i l l y , A. Osterheld, B. Pollock, and J. Tompkins
(Stanford University).
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Institute on Particle Physics, Stanford, California, ed. by A.
Mosher (1981).
6. Note that charged particle energies are determined from the constrained fit. I n addition, charged pion-kaon separation is based only on the fit.
