- Email: [email protected]
Experimental confirmation of R-meson structure
~
Nuclear Physics B3 {1967) 435-440. North-Holland Publ. Comp., Amsterdam
EXPERIMENTAL C O N F I R M A T I O N OF R-MESON STRUCTURE L. D U B A L * , M . N . F O C A C C I * , W. K I E N Z L E , C. LECHANOINE**, B. L E V R A T * , B. C. M A G L I C , M. M A R T I N * , P. S C H U B E L I N * * * ,
G. CHIKOVANI~, M. FISCHER$$, P.GRIEDER***, H. A. NEALT$$ a n d C. N E F * * * CERN. Geneva, Switzerland Received 6 September 1967
Abstract: Experimental confirmation of the structure in the region of the R(1700) meson, in the reaction y- + p --~ p + R-, reported e a r l i e r at incident pion momenta of 7 and 12 GeV/c, has been obtained at 11.5 GeV/c with the m i s s i n g - m a s s spect r o m e t e r . The peaks R1(1630), R2(1700 ) and R3(1748 ) have been observed; in addition a peak at 1830 + 15 MeV. reported by the CERN-Liverpool bubble chamber group, is indicated. Speculative comparison of our peaks and bubble chamber data with the L-excitation quark-antiquark model predictions gives a suggestive agreement in both mass separations and G - p a r i t i e s ; however, we cannot exclude this as being coincidence.
We have verified, in modified e x p e r i m e n t a l conditions, our e a r l i e r obs e r v a t i o n s a t 7 a n d 12 G e V / c (ref. [1]) of the s t r u c t u r e i n the R(1700) m e s o n , f e a t u r e d by t h r e e p e a k s - R1, R 2 a n d R 3 - at m a s s e s : MR1 = 1630 ~: 15,
MR2 = 1700 + 15,
MR3 = 1748 + 16 MeV,
(1)
with n a r r o w s w i d t h s , n e a r l y e q u a l to o u r e x p e r i m e n t a l r e s o l u t i o n , F e x p = 30 MeV. In a d d i t i o n , o u r data i n d i c a t e , b u t do not p r o v e , a f o u r t h n a r r o w p e a k a t a m a s s M = 1830 :~ 15 MeV a l r e a d y r e p o r t e d by the C E R N - L i v e r p o o l b u b b l e c h a m b e r g r o u p [2] a s a pTrTr r e s o n a n c e . E x p e r i m e n t a l c o n d i l i o n s . A s a m p l e of 2 4 0 0 0 p r o c e s s e d e v e n t s in the m i s s i n g - m a s s b a n d b e t w e e n 1.5 - 2.0 GeV i n the r e a c t i o n n - + p ~ p + R - a t the i n c i d e n t p i o n m o m e n t u m P l = 11.5 G e V / c , h a s b e e n a n a l y s e d . T h e a v e r a g e m o m e n t u m t r a n s f e r to the p r o t o n w a s t = 0.24 ( G e V / c ) 2. T h e r e w e r e t h r e e m a j o r i m p r o v e m e n t s in o u r e x p e r i m e n t a l s e t - u p ( m i s s i n g - m a s s s p e c t r o m eter): * University of Geneva, Switzerland. ** On leave from Faculty of Science, P a r i s , F r a n c e . *** Physics Institute, University of Bern, Switzerland. "~ Now at Physics Institute, Georgian Academy of Science, Tbilisi, USSR. ~- University of Lyons, F r a n c e . Joliot-Curie Fellow. J ' ~ Now at Dept. of Physics, University of Indiana, Indianapolis, USA.
436
L.DUBAL
et a l .
ID 2~
11.5 G e V / c
o
018 < t < 0.29 (GeV/c) 2 I charged
60£
C
170
11.5 G e V l c 018 < t < 0 2 9 (GeVIc) 2 (1+3) charged
Z
5~
45O
B 12.0 G e V l c 0 20 < t < o. 27 (GeV/c) 2 all Decoy Modes 350
d
3O0
°l ~ loo
A 7.0 G e V / c 0.20 < t < 0.27 {GeV/c) 2 all Decay Modes
220 50 15
116
i
1.7
I
i
l
118
19
2.0 MASS(GeV)
F i g . 1. (A) a n d (B) E a r l i e r d a t a at 7 a n d 12 G e V / c w i t h n o c h a r g e s e l e c t i o n f o r t h e d e c a y p r o d u c t s . Cf. L e v r a t et a l . [1]. T h e m o m e n t u m t r a n s f e r b i t e i s 0.20 < t < 0.27 ( G e V / c ) 2. A l t h o u g h t h i s t - r a n g e i s o u t s i d e t h e J a c o b i a n p e a k f o r t h e S(1930) m e s o n , t h e e n h a n c e m e n t at n e a r l y t h e c o r r e c t m a s s of t h e S c a n b e s e e n . (C) N e w d a t a p r o d u c e d w i t h 11.5 G e V / c i n c i d e n t ~ - w i t h a m o m e n t u m t r a n s f e r b i t e 0.18 < t < 0.29 ( G e V / c } 2. T h e c h a r g e s e l e c t i o n i s 1 + 3 c h a r g e d p a r t i c l e s in t h e v e r t e x m a t r i x . R 1, R 2, R 3 a n d S a r e c l e a r l y s e e n . F o r t h e S m e s o n a s in t h e 12 G e V / c d a t a , the t-range is partially outside the Jacobian peak. (D) N e w d a t a at 11.5 G e V / c w i t h t h e s e l e c t i o n 1 c h a r g e p a r t i c l e in t h e v e r t e x m a t r i x . C o n t r a r y to t h e a b s e n c e of R 3 in t h i s d e c a y s e l e c t i o n in o u r e a r l i e r d a t a [ s e e r e f . [1]], t h e R 3 ( 1 7 5 0 ) i s c l e a r l y s e e n , p r o b a b l y b e c a u s e of i n t r o d u c t i o n of a n e w v e r t e x m a t r i x with better resolution.
R-MESON STRUCTURE
437
110(3
i
lOOO
:~ :E 2
900
J
',i Eorlier & New DATA 7.0÷115÷120 GeVlc
800
700
600 1.5
116 117 I.'8
,
19
20
IvlAS~ (GeV)
Fig. 2. Combined e a r l i e r data (7 and 12 GeV/c} and new data. As the end of 100~ , geometrical efficiency for the 7 GeV/c data is 1.860 GeV. we plot the spectrum only up to this m a s s . (i) W h i l e in o u r p r e v i o u s w o r k , t h e p i o n m o m e n t u m w a s d e f i n e d o n l y by t h e b e a m o p t i c s to ± 1%, we h a v e t h i s t i m e m e a s u r e d the r e l a t i v e m o m e n t u m of e a c h i n c i d e n t p i o n to ±0.3%, by t h r e e n i n e - e l e m e n t b e a m h o d o s c o p e s * ; (ii) we h a v e i m p r o v e d o u r m e a s u r e m e n t of t h e r e c o i l p r o t o n m o m e n t u m by i n t r o d u c i n g a f o u r - b a n d r a n g e t e l e s c o p e , i n s t e a d of r e l y i n g p u r e l y on t i m e - o f - f l i g h t m e a s u r e m e n t s [ s e e , f o r e x a m p l e , fig. 2a in one of o u r e a r l i e r p a p e r s [4]]; (iii) we h a v e i m p r o v e d t h e m e a s u r e m e n t of t h e n u m b e r of c h a r g e d d e c a y p r o d u c t s of R, by i n t r o d u c i n g d o w n s t r e a m a n e w m a t r i x c o n s i s t i n g of 72 c r o s s e d c o u n t e r s d e f i n i n g 324 c e l l s w h o s e a r e a i n c r e a s e s a t l a r g e r a n g l e s , t h u s k e e p i n g t h e s o l i d a n g l e in t h e c . m . s y s t e m a p p r o x i m a t e l y c o n s t a n t . Elimination of experimenlal biases. T o m a k e s u r e t h a t the p e a k s a r e n o t c o n n e c t e d with the a n g u l a r p o s i t i o n of t h e s p a r k c h a m b e r s o r c o u n t e r s , we h a v e s e t t h e p r o t o n t e l e s c o p e a t 54 °, w i t h r e s p e c t to the b e a m in c o m p a r i s o n w i t h 52 ° a n d 55 ° in t h e 7 a n d 12 G e V / c r u n s , r e s p e c t i v e l y ; one d e g r e e s h i f t c o r r e s p o n d s to a b o u t 25 MeV s h i f t in m i s s i n g m a s s . T h e e v e n t s p r o d u c e d by * The principle of m e a s u r e m e n t is d e s c r i b e d in ref. [3].
438
L.DUBAL et al.
t h e K - a n d ~ c o n t a m i n a t i o n of t h e 7r- b e a m , w h i c h w a s m e a s u r e d to b e 0.6%, w e r e e l i m i n a t e d by a g a s t h r e s h o l d ~ e r e n k o v c o u n t e r , s e t f o r 7 r - t h r e s h o l d . O u r n e w d a t a a r e s h o w n in f i g . 1C, t o g e t h e r with t h e a l r e a d y r e p o r t e d d a t a of 7 G e V / c (fig. 1A) a n d 12 G e V / c (fig. 1B). T h e a p p e a r a n c e of the e n h a n c e m e n t s at the m a s s e s g i v e n in r e f . [1], w i t h i n ± 1 0 M e V , i s e v i d e n t . If the p e a k p o s i t i o n s w e r e n o t due to r e a l r e s o n a n c e s , f o r e x a m p l e if t h e m a s s v a l u e s w e r e c o n n e c t e d w i t h the v a l u e Of P l , the s h i f t f r o m 12 to 11.5 G e V / c w o u l d c a u s e a l l of t h e m to s h i f t a b o u t 50 MeV down. Dala. T h e c o m b i n e d d a t a o b t a i n e d a t 7, 12 a n d 11.5 G e V / c ( u n d e r 100% g e o m e t r i c a l e f f i c i e n c y ) a r e s h o w n in f i g . 2. T h e o n l y d i s a g r e e m e n t b e t w e e n t h e s e a n d the e a r l i e r d a t a i s t h e o b s e r v a tion of t h e R3(1748) p e a k in t h e d e c a y s e l e c t i o n "one c h a r g e d + n e u t r a l ( s ) " , w h i l e we o b s e r v e d t h a t p e a k o n l y in t h e s e l e c t i o n " t h r e e c h a r g e d + p o s s i b l e n e u t r a l ( s ) " b e f o r e . W e e x p l a i n i t a s a c o n s e q u e n c e of the i n t r o d u c t i o n of t h e n e w d e c a y m a t r i x , w h i c h h a s c o n s i d e r a b l y b e t t e r r e s o l u t i o n t h a n t h e one u s e d in p r e v i o u s r u n s , w h i c h c o n s i s t e d o n l y of 64 c e l l s . It i s c o n c e i v a b l e t h a t d e c a y m o d e s of R3 a r e q u i t e d i f f e r e n t f r o m t h o s e of the o t h e r R p e a k s , but o u r i n s t r u m e n t c a n n o t p r o v e i t . O u r m e t h o d of m e a s u r i n g the n u m b e r of c h a r g e d d e c a y p r o d u c t s i s s t i l l a r o u g h one; i t d o e s n o t p e r m i t u s to e s t a b l i s h b r a n c h i n g r a t i o s b e c a u s e we h a v e no a b s o l u t e m e a s u r e m e n t p e r m i t t i n g s o m e k i n d of n o r m a l i z a t i o n ; e a c h c h a r g e s e l e c t i o n h a s i t s own b i a s e s . F o r t h i s r e a s o n , we t u r n to b u b b l e c h a m b e r d a t a f o r the i n f o r m a t i o n on d e c a y m o d e s a n d c o n s e q u e n t l y G - p a r i t i e s of o u r p e a k s . Comparison wilh bubble c h a m b e r data. O w i n g to t h e s i m i l a r i t y of o u r m a s s s p e c t r u m in the R r e g i o n to t h e one o b s e r v e d by D a n y s z e t a l . [2] i t s e e m s r e a s o n a b l e to d i s c u s s t h e G - p a r i t i e s of o u r p e a k s by c o m p a r i n g t h e two i n d e p e n d e n t s e t s of d a t a . D a n y s z et a l . [21 o b s e r v e d two p e a k s in t h e p u t n e u t r a l s y s t e m a t m a s s 1717 + 7 MeV a n d 1832 + 6 M e V w h i c h c o u l d b e the R2(1700) a n d t h e o b s e r v e d s m a l l e n h a n c e m e n t we s e e a r o u n d 1830 M e V ; R1(1630) c a n be t h e s m a l l b u m p in the p u t s y s t e m w h i c h c a n b e s e e n in the d a t a of r e f . [2], t o o . A t t h e s a m e m a s s t h e r e w a s a 27r p e a k o b s e r v e d by C r e n n e l l et a l . [5] a n d F o r i n o et a l . [61. T h e R3(1750) i s not s e e n in t h e pTrTr d a t a . A r e a s o n a b l e e x p l a n a t i o n w o u l d b e t h a t R 3 h a s o p p o s i t e G - p a r i t y to t h e R1, R2 a n d the 1830 p e a k s , i . e . t h a t i t i s a G = -1 o b j e c t c o r r e s p o n d i n g to t h e b r o a d 3n e n h a n c e m e n t in t h i s m a s s b a n d o b s e r v e d by A r m e n i s e e t a l . [71. T h e r e a r e o t h e r b u b b l e c h a m b e r d a t a but t h e y p r e s e n t p e a k s t h a t c a n n o t e a s i l y b e d i s t i n g u i s h e d f r o m s t a t i s t i c a l fluctuations, since they show less than 4 standard deviation effects. Comparison with the quark L - e x c i l a l i o n m o d e l ( r e f . [8, 9]). I t i s i n t e r e s t i n g to n o t e t h a t on t h e b a s i s of t h e L e x c i t a t i o n m o d e l of a c h a r g e d q u a r k a n t i q u a r k (or a n y f e r m i o n - a n t i f e r m i o n ) p a i r in a D - w a v e (L = 2, I = 1), one e x p e c t s f o u r s t a t e s , t h r e e of t h e m w i t h G =+1, a n d a s i n g l e t w i t h G = - 1 , s i n c e G = ( - 1 ) L + S + I . T h e e x p e c t e d r e l a t i v e m a s s - s q u a r e d s e p a r a t i o n , A M 2, w h i c h f o l l o w s f r o m the s p i n - o r b i t f o r m u l a : A M 2 = ½ a 2 [ J ( J + l ) - L ( L +1) -S(S +1)] , i s g i v e n by:
(2)
R - M E S O N STRUCTURE
I
2S,I Lj
EXPECTED
:
I
2
I
~I
I
~I
EXPECTED, TAKINGR1ond R 3 MASSES AS INPUT DATA
MASS :
Lo~-- 2
wffh
I
OBSERVED MASS
I
2
f* 2-+2--3-
j~: Ouork -Antiquork Model
i
11
439
-
SPECTRUM
_~3 (1?z.8)[
"U C J
o
OI
by
200
MISSING- MASS Spectrometer
O ¢~ O
B O
IT-+P- P+R-
>~ 100 O
I
Bubble -Chamber i n f o r m a t i o n s on G - Pari ties given in Caption
f3_ t~
E ,,>, 0
3T P incident : L__
7s.,5.120 c~w:---.~--. ~.12o-~ I
I
1500
I
e
1700
1900
MASS (MeV)
F i g . 3. C o m b i n e d d a t a T. 11.5 and 12 G e V / c w i t h b a c k g r o u n d s u b t r a c t e d . A b o v e M == = 1.860 G e V . no 7 G e V / c d a t a w e r e p l o t t e d f o r the r e a s o n e x p l a i n e d in the c a p t i o n o f
fig. 2. U p p e r p a r t of the f i g u r e s h o w s the e x p e c t e d s p i n - o r b i t s p l i t t i n g f o r the D wave of a q u a r k - a n t i q u a r k p a i r taking the R 1 and R 3 m a s s e s a s t h e r e f e r e n c e v a l u e s . G p a r i t i e s i n f e r r e d f r o m bubble c h a m b e r e x p e r i m e n t s s u g g e s t G : 41 f o r R 1, R 2 and R 4 ; t h i s is s t r o n g l y s u p p o r t e d , p a r t i c u l a r l y f o r R1, at which m a s s a c h a r g e d dipion peak in e f f e c t i v e - m a s s d i s t r i b u t i o n h a s b e e n r e p o r t e d . The R 2 and R 4 could be i d e n t i c a l with the py~r p e a k s o b s e r v e d at the s a m e m a s s e s ; n e v e r t h e l e s s t h e s e pTrTr e n h a n c e m e n t s have only b e e n o b s e r v e d in a n e u t r a l s y s t e m and no d e f i n i t e s t a t e m e n t on i s o s p i n can be m a d e . No p o s i t i v e G - p a r i t y o b j e c t s have been found at the R 3 m a s s , but t h e r e was a b r o a d b u m p found in the 3Y n e u t r a l s y s t e m ; a s s u m i n g it is an I : 1 obj e c t . G : -1. T h e b a c k g r o u n d level xx~s d e t e r m i n e d by the s h o u l d e r s below and above the b r o a d R peak. when it was p l o t t e d in 40 MeV b i n s . 2S+ILj
= 3D 1 3D 2
1D 2
3D 3 , (2')
AM2/a2 Assuming
= -3
-1
0
+2
the splitting is due purely to L -S coupling,
let us speculate
that
440
L.DUBAL et al.
we a r e d e a l i n g with f o u r o b j e c t s * , w h o s e q u a n t u m n u m b e r s a n d m a s s e s , j P G ( m a s s ) , a r e : 1-+(1630). 2-+(1700). 2 - - ( 1 7 5 0 ) . 3-+(1820); [although C r e n n e l l et al. [5] have found f o r the 1630 MeV d i p i o n peak b e t t e r X2 with the J P = 3- h y p o t h e s i s than with the J P = 1-]. H e r e , the r e l a t i v e m a s s - s q u a r e d s e p a r a t i o n i s (1.7 ± 0.3) : 1 : (2.2 ± 0.3), to be c o m p a r e d with 2 : 1 : 2. e x p e c t e d f r o m the a b o v e L - S m a s s - s p l i t t i n g . We a s s u m e that the s e p a r a t i o n b e t w e e n R1 a n d R3 c o r r e s p o n d s to t h r e e u n i t s of L - S s p l i t t i n g . T h i s g i v e s the u n i t m a s s - s q u a r e s e p a r a t i o n , a 2, to be: a 2 = ~-(1.7482 - 1.6302 ) = 0.11 GeV 2 .
(3)
U s i n g a 2 = 0.11. we e x p e c t the m a s s e s of the o t h e r two m e m b e r s of the q u a d r u p l e t : M 2 2 = M 2 1 + 2a 2= (1707) 2 a n d s i m i l a r l y M 2 4 = (1832) 2 , to be c o m p a r e d with the o b s e r v e d MR2 = 1700 ± 15 a n d MR4 = 1830 4- 15 MeV. A l though in v i e w of m a n y m e s o n i c s t a t e s found, s u c h c o i n c i d e n c e s a r e not i m p r o b a b l e , the a g r e e m e n t i s s u g g e s t i v e . If we a s s u m e the l i n e a r , r a t h e r t h a n the m a s s - s q u a r e d d e p e n d e n c e in eq. (2) by r e p l a c i n g AM 2. the n u m e r i c a l a g r e e m e n t i s not a s good, but it i s s t i l l not f a r o u t s i d e the m a r g i n of e r r o r s on the m a s s s e p a r a t i o n b e t w e e n e a c h p a i r of p e a k s , which we take to be + 10 MeV. T h e l i n e a r u n i t s e p a r a tion b e c o m e s a = 34 MeV a n d the o b s e r v e d s e p a r a t i o n b e c o m e s (1.5 ± 0.2) : 1 : (1.7 4- 0.2). We have t a k e n the m a s s v a l u e s of the R 1 a n d R 3 p e a k s a s o u r s t a n d a r d s , to o b t a i n the u n i t s e p a r a t i o n , b e c a u s e they a r e the b e s t d e f i n e d a n d r e p r o d u c i b l e f r o m r u n to r u n (see fig. 1). We s h o u l d like to t h a n k P r o f e s s o r s W. P a u l a n d P. P r e i s w e r k f o r t h e i r c o n t i n u o u s i n t e r e s t a n d e n c o u r a g e m e n t , a n d M r . G. L a v e r r i ~ r e f o r h i s i n v a l u a b l e aid. T h e p a r t i c i p a n t s f r o m the U n i v e r s i t i e s of B e r n a n d G e n e v a a r e i n d e b t e d to the S w i s s N a t i o n a l S c i e n c e F o u n d a t i o n for i t s s u p p o r t .
RE F E R E N C E S [1] [2] [3] [4] [5] [6] [7] [81
B.Levrat et al.. Phys. Letters 22 (1966) 714, J . A . D a n y s z et al.. Phys. Letters 24B (1967) 309. H.Neal. CERN, NP Internal report 66-11. G,Chikovani et al.. Phys. Letters 25B (1967) 44. J . C , C r e n n e l l et al.. Phys. Rev. Letters 18 (1967) 323. A . F o r i n o et al.. Phys. Letters 19 (1965) 65. N.Armenise et al., Phys, Letters 25B (1967) 53. R.H.Dalitz, Proe, of XIII Int. Conf. on High-Energy Physics. Berkeley, 1966 (Univ. of Calif. Press. 1967): E . B o r e h i a n d R.Gatto. Phys. Letters 14 (1965) 352.
* In the same way Dalitz (ref. [8]) interprets 5(960), A1(1080), B(1220) and A2 (1300) as Q-Q p-wave states. [The splitting of the A 2 meson (ef. ref. [4]) has no clear interpretation in the framework of this model].
Nuclear Physics B3 {1967) 435-440. North-Holland Publ. Comp., Amsterdam
EXPERIMENTAL C O N F I R M A T I O N OF R-MESON STRUCTURE L. D U B A L * , M . N . F O C A C C I * , W. K I E N Z L E , C. LECHANOINE**, B. L E V R A T * , B. C. M A G L I C , M. M A R T I N * , P. S C H U B E L I N * * * ,
G. CHIKOVANI~, M. FISCHER$$, P.GRIEDER***, H. A. NEALT$$ a n d C. N E F * * * CERN. Geneva, Switzerland Received 6 September 1967
Abstract: Experimental confirmation of the structure in the region of the R(1700) meson, in the reaction y- + p --~ p + R-, reported e a r l i e r at incident pion momenta of 7 and 12 GeV/c, has been obtained at 11.5 GeV/c with the m i s s i n g - m a s s spect r o m e t e r . The peaks R1(1630), R2(1700 ) and R3(1748 ) have been observed; in addition a peak at 1830 + 15 MeV. reported by the CERN-Liverpool bubble chamber group, is indicated. Speculative comparison of our peaks and bubble chamber data with the L-excitation quark-antiquark model predictions gives a suggestive agreement in both mass separations and G - p a r i t i e s ; however, we cannot exclude this as being coincidence.
We have verified, in modified e x p e r i m e n t a l conditions, our e a r l i e r obs e r v a t i o n s a t 7 a n d 12 G e V / c (ref. [1]) of the s t r u c t u r e i n the R(1700) m e s o n , f e a t u r e d by t h r e e p e a k s - R1, R 2 a n d R 3 - at m a s s e s : MR1 = 1630 ~: 15,
MR2 = 1700 + 15,
MR3 = 1748 + 16 MeV,
(1)
with n a r r o w s w i d t h s , n e a r l y e q u a l to o u r e x p e r i m e n t a l r e s o l u t i o n , F e x p = 30 MeV. In a d d i t i o n , o u r data i n d i c a t e , b u t do not p r o v e , a f o u r t h n a r r o w p e a k a t a m a s s M = 1830 :~ 15 MeV a l r e a d y r e p o r t e d by the C E R N - L i v e r p o o l b u b b l e c h a m b e r g r o u p [2] a s a pTrTr r e s o n a n c e . E x p e r i m e n t a l c o n d i l i o n s . A s a m p l e of 2 4 0 0 0 p r o c e s s e d e v e n t s in the m i s s i n g - m a s s b a n d b e t w e e n 1.5 - 2.0 GeV i n the r e a c t i o n n - + p ~ p + R - a t the i n c i d e n t p i o n m o m e n t u m P l = 11.5 G e V / c , h a s b e e n a n a l y s e d . T h e a v e r a g e m o m e n t u m t r a n s f e r to the p r o t o n w a s t = 0.24 ( G e V / c ) 2. T h e r e w e r e t h r e e m a j o r i m p r o v e m e n t s in o u r e x p e r i m e n t a l s e t - u p ( m i s s i n g - m a s s s p e c t r o m eter): * University of Geneva, Switzerland. ** On leave from Faculty of Science, P a r i s , F r a n c e . *** Physics Institute, University of Bern, Switzerland. "~ Now at Physics Institute, Georgian Academy of Science, Tbilisi, USSR. ~- University of Lyons, F r a n c e . Joliot-Curie Fellow. J ' ~ Now at Dept. of Physics, University of Indiana, Indianapolis, USA.
436
L.DUBAL
et a l .
ID 2~
11.5 G e V / c
o
018 < t < 0.29 (GeV/c) 2 I charged
60£
C
170
11.5 G e V l c 018 < t < 0 2 9 (GeVIc) 2 (1+3) charged
Z
5~
45O
B 12.0 G e V l c 0 20 < t < o. 27 (GeV/c) 2 all Decoy Modes 350
d
3O0
°l ~ loo
A 7.0 G e V / c 0.20 < t < 0.27 {GeV/c) 2 all Decay Modes
220 50 15
116
i
1.7
I
i
l
118
19
2.0 MASS(GeV)
F i g . 1. (A) a n d (B) E a r l i e r d a t a at 7 a n d 12 G e V / c w i t h n o c h a r g e s e l e c t i o n f o r t h e d e c a y p r o d u c t s . Cf. L e v r a t et a l . [1]. T h e m o m e n t u m t r a n s f e r b i t e i s 0.20 < t < 0.27 ( G e V / c ) 2. A l t h o u g h t h i s t - r a n g e i s o u t s i d e t h e J a c o b i a n p e a k f o r t h e S(1930) m e s o n , t h e e n h a n c e m e n t at n e a r l y t h e c o r r e c t m a s s of t h e S c a n b e s e e n . (C) N e w d a t a p r o d u c e d w i t h 11.5 G e V / c i n c i d e n t ~ - w i t h a m o m e n t u m t r a n s f e r b i t e 0.18 < t < 0.29 ( G e V / c } 2. T h e c h a r g e s e l e c t i o n i s 1 + 3 c h a r g e d p a r t i c l e s in t h e v e r t e x m a t r i x . R 1, R 2, R 3 a n d S a r e c l e a r l y s e e n . F o r t h e S m e s o n a s in t h e 12 G e V / c d a t a , the t-range is partially outside the Jacobian peak. (D) N e w d a t a at 11.5 G e V / c w i t h t h e s e l e c t i o n 1 c h a r g e p a r t i c l e in t h e v e r t e x m a t r i x . C o n t r a r y to t h e a b s e n c e of R 3 in t h i s d e c a y s e l e c t i o n in o u r e a r l i e r d a t a [ s e e r e f . [1]], t h e R 3 ( 1 7 5 0 ) i s c l e a r l y s e e n , p r o b a b l y b e c a u s e of i n t r o d u c t i o n of a n e w v e r t e x m a t r i x with better resolution.
R-MESON STRUCTURE
437
110(3
i
lOOO
:~ :E 2
900
J
',i Eorlier & New DATA 7.0÷115÷120 GeVlc
800
700
600 1.5
116 117 I.'8
,
19
20
IvlAS~ (GeV)
Fig. 2. Combined e a r l i e r data (7 and 12 GeV/c} and new data. As the end of 100~ , geometrical efficiency for the 7 GeV/c data is 1.860 GeV. we plot the spectrum only up to this m a s s . (i) W h i l e in o u r p r e v i o u s w o r k , t h e p i o n m o m e n t u m w a s d e f i n e d o n l y by t h e b e a m o p t i c s to ± 1%, we h a v e t h i s t i m e m e a s u r e d the r e l a t i v e m o m e n t u m of e a c h i n c i d e n t p i o n to ±0.3%, by t h r e e n i n e - e l e m e n t b e a m h o d o s c o p e s * ; (ii) we h a v e i m p r o v e d o u r m e a s u r e m e n t of t h e r e c o i l p r o t o n m o m e n t u m by i n t r o d u c i n g a f o u r - b a n d r a n g e t e l e s c o p e , i n s t e a d of r e l y i n g p u r e l y on t i m e - o f - f l i g h t m e a s u r e m e n t s [ s e e , f o r e x a m p l e , fig. 2a in one of o u r e a r l i e r p a p e r s [4]]; (iii) we h a v e i m p r o v e d t h e m e a s u r e m e n t of t h e n u m b e r of c h a r g e d d e c a y p r o d u c t s of R, by i n t r o d u c i n g d o w n s t r e a m a n e w m a t r i x c o n s i s t i n g of 72 c r o s s e d c o u n t e r s d e f i n i n g 324 c e l l s w h o s e a r e a i n c r e a s e s a t l a r g e r a n g l e s , t h u s k e e p i n g t h e s o l i d a n g l e in t h e c . m . s y s t e m a p p r o x i m a t e l y c o n s t a n t . Elimination of experimenlal biases. T o m a k e s u r e t h a t the p e a k s a r e n o t c o n n e c t e d with the a n g u l a r p o s i t i o n of t h e s p a r k c h a m b e r s o r c o u n t e r s , we h a v e s e t t h e p r o t o n t e l e s c o p e a t 54 °, w i t h r e s p e c t to the b e a m in c o m p a r i s o n w i t h 52 ° a n d 55 ° in t h e 7 a n d 12 G e V / c r u n s , r e s p e c t i v e l y ; one d e g r e e s h i f t c o r r e s p o n d s to a b o u t 25 MeV s h i f t in m i s s i n g m a s s . T h e e v e n t s p r o d u c e d by * The principle of m e a s u r e m e n t is d e s c r i b e d in ref. [3].
438
L.DUBAL et al.
t h e K - a n d ~ c o n t a m i n a t i o n of t h e 7r- b e a m , w h i c h w a s m e a s u r e d to b e 0.6%, w e r e e l i m i n a t e d by a g a s t h r e s h o l d ~ e r e n k o v c o u n t e r , s e t f o r 7 r - t h r e s h o l d . O u r n e w d a t a a r e s h o w n in f i g . 1C, t o g e t h e r with t h e a l r e a d y r e p o r t e d d a t a of 7 G e V / c (fig. 1A) a n d 12 G e V / c (fig. 1B). T h e a p p e a r a n c e of the e n h a n c e m e n t s at the m a s s e s g i v e n in r e f . [1], w i t h i n ± 1 0 M e V , i s e v i d e n t . If the p e a k p o s i t i o n s w e r e n o t due to r e a l r e s o n a n c e s , f o r e x a m p l e if t h e m a s s v a l u e s w e r e c o n n e c t e d w i t h the v a l u e Of P l , the s h i f t f r o m 12 to 11.5 G e V / c w o u l d c a u s e a l l of t h e m to s h i f t a b o u t 50 MeV down. Dala. T h e c o m b i n e d d a t a o b t a i n e d a t 7, 12 a n d 11.5 G e V / c ( u n d e r 100% g e o m e t r i c a l e f f i c i e n c y ) a r e s h o w n in f i g . 2. T h e o n l y d i s a g r e e m e n t b e t w e e n t h e s e a n d the e a r l i e r d a t a i s t h e o b s e r v a tion of t h e R3(1748) p e a k in t h e d e c a y s e l e c t i o n "one c h a r g e d + n e u t r a l ( s ) " , w h i l e we o b s e r v e d t h a t p e a k o n l y in t h e s e l e c t i o n " t h r e e c h a r g e d + p o s s i b l e n e u t r a l ( s ) " b e f o r e . W e e x p l a i n i t a s a c o n s e q u e n c e of the i n t r o d u c t i o n of t h e n e w d e c a y m a t r i x , w h i c h h a s c o n s i d e r a b l y b e t t e r r e s o l u t i o n t h a n t h e one u s e d in p r e v i o u s r u n s , w h i c h c o n s i s t e d o n l y of 64 c e l l s . It i s c o n c e i v a b l e t h a t d e c a y m o d e s of R3 a r e q u i t e d i f f e r e n t f r o m t h o s e of the o t h e r R p e a k s , but o u r i n s t r u m e n t c a n n o t p r o v e i t . O u r m e t h o d of m e a s u r i n g the n u m b e r of c h a r g e d d e c a y p r o d u c t s i s s t i l l a r o u g h one; i t d o e s n o t p e r m i t u s to e s t a b l i s h b r a n c h i n g r a t i o s b e c a u s e we h a v e no a b s o l u t e m e a s u r e m e n t p e r m i t t i n g s o m e k i n d of n o r m a l i z a t i o n ; e a c h c h a r g e s e l e c t i o n h a s i t s own b i a s e s . F o r t h i s r e a s o n , we t u r n to b u b b l e c h a m b e r d a t a f o r the i n f o r m a t i o n on d e c a y m o d e s a n d c o n s e q u e n t l y G - p a r i t i e s of o u r p e a k s . Comparison wilh bubble c h a m b e r data. O w i n g to t h e s i m i l a r i t y of o u r m a s s s p e c t r u m in the R r e g i o n to t h e one o b s e r v e d by D a n y s z e t a l . [2] i t s e e m s r e a s o n a b l e to d i s c u s s t h e G - p a r i t i e s of o u r p e a k s by c o m p a r i n g t h e two i n d e p e n d e n t s e t s of d a t a . D a n y s z et a l . [21 o b s e r v e d two p e a k s in t h e p u t n e u t r a l s y s t e m a t m a s s 1717 + 7 MeV a n d 1832 + 6 M e V w h i c h c o u l d b e the R2(1700) a n d t h e o b s e r v e d s m a l l e n h a n c e m e n t we s e e a r o u n d 1830 M e V ; R1(1630) c a n be t h e s m a l l b u m p in the p u t s y s t e m w h i c h c a n b e s e e n in the d a t a of r e f . [2], t o o . A t t h e s a m e m a s s t h e r e w a s a 27r p e a k o b s e r v e d by C r e n n e l l et a l . [5] a n d F o r i n o et a l . [61. T h e R3(1750) i s not s e e n in t h e pTrTr d a t a . A r e a s o n a b l e e x p l a n a t i o n w o u l d b e t h a t R 3 h a s o p p o s i t e G - p a r i t y to t h e R1, R2 a n d the 1830 p e a k s , i . e . t h a t i t i s a G = -1 o b j e c t c o r r e s p o n d i n g to t h e b r o a d 3n e n h a n c e m e n t in t h i s m a s s b a n d o b s e r v e d by A r m e n i s e e t a l . [71. T h e r e a r e o t h e r b u b b l e c h a m b e r d a t a but t h e y p r e s e n t p e a k s t h a t c a n n o t e a s i l y b e d i s t i n g u i s h e d f r o m s t a t i s t i c a l fluctuations, since they show less than 4 standard deviation effects. Comparison with the quark L - e x c i l a l i o n m o d e l ( r e f . [8, 9]). I t i s i n t e r e s t i n g to n o t e t h a t on t h e b a s i s of t h e L e x c i t a t i o n m o d e l of a c h a r g e d q u a r k a n t i q u a r k (or a n y f e r m i o n - a n t i f e r m i o n ) p a i r in a D - w a v e (L = 2, I = 1), one e x p e c t s f o u r s t a t e s , t h r e e of t h e m w i t h G =+1, a n d a s i n g l e t w i t h G = - 1 , s i n c e G = ( - 1 ) L + S + I . T h e e x p e c t e d r e l a t i v e m a s s - s q u a r e d s e p a r a t i o n , A M 2, w h i c h f o l l o w s f r o m the s p i n - o r b i t f o r m u l a : A M 2 = ½ a 2 [ J ( J + l ) - L ( L +1) -S(S +1)] , i s g i v e n by:
(2)
R - M E S O N STRUCTURE
I
2S,I Lj
EXPECTED
:
I
2
I
~I
I
~I
EXPECTED, TAKINGR1ond R 3 MASSES AS INPUT DATA
MASS :
Lo~-- 2
wffh
I
OBSERVED MASS
I
2
f* 2-+2--3-
j~: Ouork -Antiquork Model
i
11
439
-
SPECTRUM
_~3 (1?z.8)[
"U C J
o
OI
by
200
MISSING- MASS Spectrometer
O ¢~ O
B O
IT-+P- P+R-
>~ 100 O
I
Bubble -Chamber i n f o r m a t i o n s on G - Pari ties given in Caption
f3_ t~
E ,,>, 0
3T P incident : L__
7s.,5.120 c~w:---.~--. ~.12o-~ I
I
1500
I
e
1700
1900
MASS (MeV)
F i g . 3. C o m b i n e d d a t a T. 11.5 and 12 G e V / c w i t h b a c k g r o u n d s u b t r a c t e d . A b o v e M == = 1.860 G e V . no 7 G e V / c d a t a w e r e p l o t t e d f o r the r e a s o n e x p l a i n e d in the c a p t i o n o f
fig. 2. U p p e r p a r t of the f i g u r e s h o w s the e x p e c t e d s p i n - o r b i t s p l i t t i n g f o r the D wave of a q u a r k - a n t i q u a r k p a i r taking the R 1 and R 3 m a s s e s a s t h e r e f e r e n c e v a l u e s . G p a r i t i e s i n f e r r e d f r o m bubble c h a m b e r e x p e r i m e n t s s u g g e s t G : 41 f o r R 1, R 2 and R 4 ; t h i s is s t r o n g l y s u p p o r t e d , p a r t i c u l a r l y f o r R1, at which m a s s a c h a r g e d dipion peak in e f f e c t i v e - m a s s d i s t r i b u t i o n h a s b e e n r e p o r t e d . The R 2 and R 4 could be i d e n t i c a l with the py~r p e a k s o b s e r v e d at the s a m e m a s s e s ; n e v e r t h e l e s s t h e s e pTrTr e n h a n c e m e n t s have only b e e n o b s e r v e d in a n e u t r a l s y s t e m and no d e f i n i t e s t a t e m e n t on i s o s p i n can be m a d e . No p o s i t i v e G - p a r i t y o b j e c t s have been found at the R 3 m a s s , but t h e r e was a b r o a d b u m p found in the 3Y n e u t r a l s y s t e m ; a s s u m i n g it is an I : 1 obj e c t . G : -1. T h e b a c k g r o u n d level xx~s d e t e r m i n e d by the s h o u l d e r s below and above the b r o a d R peak. when it was p l o t t e d in 40 MeV b i n s . 2S+ILj
= 3D 1 3D 2
1D 2
3D 3 , (2')
AM2/a2 Assuming
= -3
-1
0
+2
the splitting is due purely to L -S coupling,
let us speculate
that
440
L.DUBAL et al.
we a r e d e a l i n g with f o u r o b j e c t s * , w h o s e q u a n t u m n u m b e r s a n d m a s s e s , j P G ( m a s s ) , a r e : 1-+(1630). 2-+(1700). 2 - - ( 1 7 5 0 ) . 3-+(1820); [although C r e n n e l l et al. [5] have found f o r the 1630 MeV d i p i o n peak b e t t e r X2 with the J P = 3- h y p o t h e s i s than with the J P = 1-]. H e r e , the r e l a t i v e m a s s - s q u a r e d s e p a r a t i o n i s (1.7 ± 0.3) : 1 : (2.2 ± 0.3), to be c o m p a r e d with 2 : 1 : 2. e x p e c t e d f r o m the a b o v e L - S m a s s - s p l i t t i n g . We a s s u m e that the s e p a r a t i o n b e t w e e n R1 a n d R3 c o r r e s p o n d s to t h r e e u n i t s of L - S s p l i t t i n g . T h i s g i v e s the u n i t m a s s - s q u a r e s e p a r a t i o n , a 2, to be: a 2 = ~-(1.7482 - 1.6302 ) = 0.11 GeV 2 .
(3)
U s i n g a 2 = 0.11. we e x p e c t the m a s s e s of the o t h e r two m e m b e r s of the q u a d r u p l e t : M 2 2 = M 2 1 + 2a 2= (1707) 2 a n d s i m i l a r l y M 2 4 = (1832) 2 , to be c o m p a r e d with the o b s e r v e d MR2 = 1700 ± 15 a n d MR4 = 1830 4- 15 MeV. A l though in v i e w of m a n y m e s o n i c s t a t e s found, s u c h c o i n c i d e n c e s a r e not i m p r o b a b l e , the a g r e e m e n t i s s u g g e s t i v e . If we a s s u m e the l i n e a r , r a t h e r t h a n the m a s s - s q u a r e d d e p e n d e n c e in eq. (2) by r e p l a c i n g AM 2. the n u m e r i c a l a g r e e m e n t i s not a s good, but it i s s t i l l not f a r o u t s i d e the m a r g i n of e r r o r s on the m a s s s e p a r a t i o n b e t w e e n e a c h p a i r of p e a k s , which we take to be + 10 MeV. T h e l i n e a r u n i t s e p a r a tion b e c o m e s a = 34 MeV a n d the o b s e r v e d s e p a r a t i o n b e c o m e s (1.5 ± 0.2) : 1 : (1.7 4- 0.2). We have t a k e n the m a s s v a l u e s of the R 1 a n d R 3 p e a k s a s o u r s t a n d a r d s , to o b t a i n the u n i t s e p a r a t i o n , b e c a u s e they a r e the b e s t d e f i n e d a n d r e p r o d u c i b l e f r o m r u n to r u n (see fig. 1). We s h o u l d like to t h a n k P r o f e s s o r s W. P a u l a n d P. P r e i s w e r k f o r t h e i r c o n t i n u o u s i n t e r e s t a n d e n c o u r a g e m e n t , a n d M r . G. L a v e r r i ~ r e f o r h i s i n v a l u a b l e aid. T h e p a r t i c i p a n t s f r o m the U n i v e r s i t i e s of B e r n a n d G e n e v a a r e i n d e b t e d to the S w i s s N a t i o n a l S c i e n c e F o u n d a t i o n for i t s s u p p o r t .
RE F E R E N C E S [1] [2] [3] [4] [5] [6] [7] [81
B.Levrat et al.. Phys. Letters 22 (1966) 714, J . A . D a n y s z et al.. Phys. Letters 24B (1967) 309. H.Neal. CERN, NP Internal report 66-11. G,Chikovani et al.. Phys. Letters 25B (1967) 44. J . C , C r e n n e l l et al.. Phys. Rev. Letters 18 (1967) 323. A . F o r i n o et al.. Phys. Letters 19 (1965) 65. N.Armenise et al., Phys, Letters 25B (1967) 53. R.H.Dalitz, Proe, of XIII Int. Conf. on High-Energy Physics. Berkeley, 1966 (Univ. of Calif. Press. 1967): E . B o r e h i a n d R.Gatto. Phys. Letters 14 (1965) 352.
* In the same way Dalitz (ref. [8]) interprets 5(960), A1(1080), B(1220) and A2 (1300) as Q-Q p-wave states. [The splitting of the A 2 meson (ef. ref. [4]) has no clear interpretation in the framework of this model].