- Email: [email protected]
Observation of a (Kππ) resonance near 1800 MeV
Volume 22, n u m b e r 3
PHYSICS
14. See, eg.: C.Alff, D. Berley, D. Colley, N.Gelfand, U. Nauenberg, D . M i l l e r , J. Schultz, J . S t e i n b e r g e r , T. H. Tan, H, B r u g g e r , P. K r a m e r and R. Plane, Phys. Rev. L e t t e r s 9 (1962) 325; B. Buschbeck-Czapp, I. Wacek, W.A. Cooper, A. F r i d m a n , E . M a l a m u d , G . O t t e r , E . G e l s e m a and A. T e n n e r , P r e c . of the Sienna Intern. Conf. on E l e m e n t a r y P a r t i c l e s (1963) 166; N. Gelfand, D . M i l l e r , M. Nussbaum, J. Ratau, J. Schultz, J. Steinberger, T.H. Tan, L. K i r s c h and R. Plane, Phys. Rev. L e t t e r s 11 (1963) 463; J. J. M u r r a y J r . , M. F e r r o _ L u z z i , D.O. Huwe, J. B. Schafer, F . T . Solmitz and M. Lynn Stevenson, P h y s i c s L e t t e r s 7 (1963) 358;
OBSERVATION
OF
LETTERS
R. Kraemer, L. Madansky, M. Meer. M. Nussbaum. A. Pevsner. C. Richardson, R.Strand. R. Zdnnis. T, Fields, S.Orenstein and T. Toohig, Phys. Rev. 136 (1964) B496; S . M . F l a t t e , D.O.Huwe, J . J . M u r r a y . J . B u t t o n Shafer, F . T . Solmitz, M. Lynn Stevenson and C. Wohl, Phys. Rev. L e t t e r s 14 (1965) 1095. 15. M. Gell-Mann, D. Sharp and W. G, Wagner, Phys. Rev. L e t t e r s 8 (1962) 261; W. E. T h i r r i n g , P h y i c s L e t t e r s 16 (1965) 335; C. Becchi and G. Morpurgo, Phys. Rev. 140 (1965) B687; S. K. Kundu, Phys. Rev. 141 (1966) 1529.
A (K~z) R E S O N A N C E
Aachen-Berlin-CERN-London
15 August 1966
NEAR
(I.C.)-Vienna
1800
MeV
Collaboration
J. BARTSCH, M. D E U T S C H M A N N , E. K E P P E L , G. K R A U S
and R. S P E T H Physikalisches Institut der Technischen Hochschule, Aachen, Germany C. G R O T E , J. K L U G O W , D. P O S E , H. S C H I L L E R and H. V O G T Forschungsstelle flit Physih Hoher Energien der Deutschen Akadernie der Wissenschaften zu Berlin, Zeuthen, Germany
M. BARDADIN-OTWINOWSKA *, V. T. C O C C O N I , P. F. D A L P I A Z **, E. F L A M I N I O * * * , J. D. H A N S E N ~, H. H R O M A D N I K ~ , G. K E L L N E R , D.R.O. MORRISON and S. N O W A K % ~ CERN, European Organization f o r Nuclear Research, Geneva N. C. B A R F O R D ,
D. P. D A L L M A N , S. J. G O L D S A C K , M.E. MERMIKIDES Physics Department, Imperial College, London
and N. C. M U K H E R J E E
A. F R O H L I C H , G. O T T E R , I.W A C E K and H. W A H L Institut f~r Theoretische Physik der Universit~it, Vienna Received 11 July 1966 Both in the reaction K-p --~pK-ff+~"- and in the reaction K-p --*pK°ff-Tt°induced by I0 GeV/c negative kaons on hydrogen, an enhancement is observed in the (Kffff)-effectivemass distribution, at mass M = 1789 • 10 M e V and with fullwidth at half height r = 80 +240 MeV. Evidence is presented which is consistentwith the interpretationof this enhancement as a resonk5~ state of isospin I = ½, with possible decay modes into Kp, K*ff and Zc0. It is proposed to name this resonance the L-meson.
A b o u t 200 000 p h o t o g r a p h s of 10 G e V / c n e g a t i v e k a o n s , w i t h a n a v e r a g e of 5 k a o n s / p i c t u r e , were taken at the CERN proton-synchrotron in t h e 150 c m B r i t i s h h y d r o g e n b u b b l e c h a m b e r . This was the first experiment performed with a h i g h e n e r g y r a d i o - f r e q u e n c y s e p a r a t e d b e a m [1]. The events with 2 and 4 prongs, whether or not a strange particle is seen to decay, were measured on IEP or similar machines and aria-
* ** *** t t?
On leave f r o m the University of Warsaw. CERN Fellow f r o m the University of Bologna. CERN Fellow f r o m the University of P i s a . CERN Fellow f r o m the U n i v e r s i t y of Copenhagen. CERN Fellow f r o m the Institut f u r T h e o r e t i s c h e Physik, Vienna. t~t On leave from the Forschungsstelle fur Physik Hoher Energien, Berlin-Zeuthen.
35'7
Volume 22, number 3
PHYSICS LETTERS
l y s e d with the T H R E S H - G R I N D - S L I C E - S U M X s y s t e m of p r o g r a m s . Out of ~9000 e v e n t s f o r which k i n e m a t i c f i t s w e r e obtained, 994 e v e n t s w e r e c l a s s i f i e d $ as belonging to the r e a c t i o n :
15 August 1966
R e a c t i o n s (1) and (2), t h e r e f o r e , p a r t l y p r o c e e d v i a f o r m a t i o n of the two-body i n t e r m e d i a t e state: K ' p -~ p L - .
K- p ~ pK-Tr+~ and 425 e v e n t s to the r e a c t i o n : K- p ~ pK°Tr'Tr ° .
(2)
Since in the r e a c t i o n (1) the p o s i t i v e pion f r e quently c o m b i n e s with the p r o t o n to f o r m the N*++(1238) i s o b a r , in the following a n a l y s i s of the (KTr~) s y s t e m only 699 e v e n t s of this r e a c t i o n have been used, f o r which no (pTr+) c o m b i n a t i o n is in the m a s s r e g i o n 1.12 to 1.34 GeV. In fig. l a and Ib a r e shown the (KTrTr)- e f f e c t i v e m a s s d i s t r i butions f o r r e a c t i o n (i), N*++ excluded, and f o r r e a c t i o n (2). The shaded a r e a s c o r r e s p o n d to the e v e n t s f o r which the s q u a r e f o u r - m o m e n t u m , It I, t r a n s f e r r e d to the proton, s a t i s f i e s the condition Itl < 0.6 (GeV/c) 2. In fig. Ic is shown the s u m of t h e s e d i s t r i b u t i o n s f o r It] < 0.6 (GeV/c) 2. It can be s e e n in the f i g u r e s that t h e r e is a b r o a d peak n e a r 1330 MeV and a n a r r o w e r peak n e a r 1800 MeV. The f i r s t peak m a y contain s e v e r a l of the e n h a n c e m e n t s r e p o r t e d in the l i t e r a t u r e *. In this l e t t e r we a r e c o n c e r n e d with the second peak which is o b s e r v e d h e r e f o r the first time. Since t h e r e e x i s t s at p r e s e n t no adequate m e a n s of c a l c u l a t i n g the shape of the n o n - r e s o nant b a c k g r o u n d in the d i s t r i b u t i o n of fig. l c , s e v e r a l " b a c k g r o u n d s " have been drawn by hand in the r e g i o n M ( I ~ ) > 1.50 GeV, and f i t s have been made to the e x p e r i m e n t a l d i s t r i b u t i o n in fig. l c with such background s h a p e s and with a B r e i t - W i g n e r c u r v e to d e s c r i b e the peak n e a r 1800 MeV. The f i t s i n d i c a t e that the (K~lr) e n h a n c e m e n t o c c u r s at a m a s s M = 1789 ~- l ~ / I e V , and has a full width at half height r = 80 _+~ MeV. The e r r o r s g i v en above contain a ll o w a n c e f o r the s y s t e m a t i c u n c e r t a i n t y d e r i v i n g f r o m the l a c k of knowledge of the t r u e background shape. The a s y m m e t r i c e r r o r in F d e r i v e s f r o m the f a c t that the e x p e r i m e n t a l r e s o l u t i o n is not m u c h s m a l l e r than the peak width i t s e l f **. In the m a s s r e g i o n of the e n h a n c e m e n t (1.71 to 1.87 GeV), the b a c k ground a c c o u n t s f o r 40 to 50%, depending on the b a c k g r o u n d ch o s en , of the e v e n t s o b s e r v e d , and the peak stands 5 to 7 s t a n d a r d d e v i a t i o n s above background. As our d a t a o f f er no o t h e r explanation of this e n h a n c e m e n t (e.g. r e f l e c t i o n o r o t h e r k i n e m a t i c effect), we a r e led to conclude that t h e r e e x i s t s a K~v r e s o n a n t state at this m a s s and p r o p o s e to n a m e it the L-meson.
358
(3)
(1) It may be noted that the r e s t r i c t i o n to s m a l l It ] does not a l t e r s u b s t a n t i a l l y the n u m b e r of e v e n t s i n t h e L - m e s o n r eg i o n . The c r o s s s e c t i o n f o r the p r o d u c t i o n of the L m e s o n in r e a c t i o n (3) is of the o r d e r of 100 ~b. The i s o s p i n of this r e s o n a n c e can be I = ½ or ~2. Some p o s s i b l e d e c a y m o d e s of the L - m e s o n a r e s u g g e s t e d by the d i s t r i b u t i o n s in fig. 2. Fig. 2a shows ~he 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 f o r the s y s t e m (K-w) as obtained f r o m the e v e n t s of r e a c t i o n : K - p ~pK-Tr+Tr-Tr ° ,
(4)
by excluding N*++(1238) and r e q u i r i n g that the t h r e e - p i o n s y s t e m be in the m a s s r e g i o n of the o m e g a - m e s o n (0.75 to 0.81 GeV). Fig. 2b shows the (Ky)- m a s s d i s t r i b u t i o n f o r the e v e n t s of the reactions: K ' p ~pK-Tr ° ,
(5)
K-p~p~°-
(6)
.
The d i s t r i b u t i o n in fig. 2c is obtained f o r the e v e n t s of r e a c t i o n s (1) and (2) by set t i n g the c o n ditions that the d i - p i o n s y s t e m s c o n s i d e r e d a r e t h o se with e f f e c t i v e m a s s in the r e g i o n of the r h o - m e s o n (0.62 to 0.88 GeV) and the d i s t r i b u t i o n in fig. 2d is s i m i l a r l y obtained by r e q u i r i n g that the (K~) s y s t e m s c o n s i d e r e d a r e t h o se with e f f e c t i v e m a s s in the r e g i o n of the K*(890) r e s o n a n c e (0.85 to 0.93 GeV). It can be s e e n that the d i s t r i b u t i o n s in fig. 2a, 2c and 2d all p r e s e n t e n h a n c e m e n t s at around 1300 MeV and 1800 MeV, while no e n h a n c e m e n t s at those m a s s e s a r e s e e n in fig. 2b, w h e r e , howe v e r , the r e s o n a n c e s K*(890) and K*(1400) stand out c l e a r l y . Thus, no e v i d e n c e is obtained f o r the d ecay L ~ Ky, while the r e s u l t s in fig. 2a m ay be c o n s i d e r e d as e v i d e n c e f o r the d ecay L - - Kw. In fact, in the m a s s r e g i o n of the L - m e s o n , 2 e v e n t s $ The fiducial region in which events of reaction (2) were studied is about twice as large as the region in which events of reaction (1) were taken. * For a summary of the references on (K~'y) resonances with mass of 1170, 1215, 1275, 1320 and 1400 MeV, see ref. 2. ** The experimental resolution in this experiment is of 40 MeV, as estimated from the fitted value of the full width at half height of the omega-peak observed in the effective mass distribution of the three-pion system in reaction K-p ~ pK- w+y-11° .
V o l u m e 22, n u m b e r 3
K-p
PHYSICS
INTERACTIONS
=)
15 A u g u s t 1966
AT 10 GeVIc
p K'e÷Tr" 4( --~
LETTERS
~ lo
O)
o
K ' P - - pK'u) - - PK'tf*ff'lle T
~
• It I
i
20
(Kw)" [FFEC'n~ MASS.
>ao NO b)
K p--,,pfl'K°oBs. PLUS • K ' p ~ prr K"
l
o :[
AT 1 0 ~ 1 ¢
N ~ + ÷ EXCLUDED 699 EVENTS
0
AT 10G~Ic 2
o
maT
~
Z
v
~
~
w> 2( LLI
iv.
Itl
o
u.I m
|K~o)-EFFECTNE MASS, GeV
Z
.
4c
.
.
.
d) ~ K-p~PK~-II'-"PK*lT-'w* I L~ PLUS [ ] KK~'-~ pK-n''n- (NON~'~')
1.0
(K1TTf)
2.0 EFF.
3.0
i
2
(l~W)- EFFECTNE MASS,GeV
MASS,GeV
F i g . 1. a) 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 of t h e ( K n z 0 - s y s t e m f o r e v e n t s of r e a c t i o n (1) f o r w h i c h t h e (pTr +) s y s t e m i s n o t in t h e m a s s r e g i o n of t h e N*. T h e s h a d e d a r e a c o r r e s p o n d s to t h e e v e n t s with I t I < 0.6 (GeV/c) 2. b) 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 of the (K~rn)- s y s t e m f o r the e v e n t s of r e a c t i o n (2). T h e s h a d e d a r e a c o r r e s p o n d s to the e v e n t s with I tl < 0.6 (GeV/c) 2. c) S u m of t h e two a b o v e d i s t r i b u t i o n s , f o r t h e e v e n t s in w h i c h t h e s q u a r e d f o u r m o m e n t u m t r a n s f e r r e d to t h e p r o t o n is I tl < 0.6 (GeV/c) 2.
F i g . 2. a) (Kc0)- 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 obtained f r o m r e a c t i o n (4). b) (KTr)- 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 o b t a i n e d f r o m r e a c t i o n s (5) and (6). c) ( K p ) - 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 o b t a i n e d f r o m r e a c t i o n s (1) and (2). d) ( K * ~ ) - 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 obtained f r o m r e a c t i o n s (1) and (2).
359
Volume 22, n u m b e r 3
PHYSICS
LETTERS
15 August 1966
Table 1 Expected values of the r a t i o s indicated, for isospin ½ and ~ of the L - m e s o n , and corresponding e x p e r i m e n t a l values deduced f r o m r e a c t i o n s (1) and (2). The expected values a r e calculated c o r r e c t i n g for unobservable decay modes, probability of detecting the K ° and difference in size of fiducial regions for r e a c t i o n s (1) and (2). Isospin of L-meson
K* -(S90)~"° --, (K°Tr-) ?To
K*O(890)~.- --, (K-~+)~.- + (KOy°)~"-
K*O(S90)y- --, (K°~.°) 7r-
K* -(890)7 ° -'~ (K°Tr-) ?r°
Theo r.
Expt.
Theor.
Expt.
1 2
0.9 + 0.6
a r e e x p e c t e d f r o m t h e b a c k g r o u n d , a n d 12 e v e n t s a r e o b s e r v e d . T h e e x i s t e n c e of t h e d e c a y L --* Kw w o u l d i m p l y t h a t t h e i s o s p i n of t h e L - m e s o n i s [=1~. T h e e n h a n c e m e n t s o b s e r v e d a t a r o u n d 1800 M e V i n t h e (Kp) a n d (K*~) m a s s d i s t r i b u t i o n d o not prove, but are consistent with the decays L ~ K p a n d L -~ K*~. If t h e a s s u m p t i o n i s m a d e t h a t t h e e n h a n c e m e n t s a t 1800 M e V o b s e r v e d i n t h e v a r i o u s c h a r g e s t a t e s of (K*~) m a s s d i s t r i b u t i o n s do r e p r e s e n t t h e d e c a y L ~ K*~, t h e n t h e d a t a c o n f i r m t h e a s s i g n m e n t I =~.1 T h i s i s s h o w n i n t a b l e 1, w h e r e t h e e x p e r i m e n t a l v a l u e s f o r t h e ratios indicated are given along with the values e x p e c t e d f o r I = ½ a n d I = ~. A K~ resonance cannot have spin and parity, JP = 0 +. If t h e d e c a y L ~ Ky r e a l l y d o e s n o t e x i s t , it may be that the L-meson has spin and parity incompatible with such a decay, i.e., that the Lm e s o n h a s JP i n t h e s e r i e s 0 - , 1 +, 2 - , . . .
360
3.0 :e 1.5
We are deeply indebted to the operating crews of t h e C E R N p r o t o n s y n c h r o t r o n , of t h e 150 c m British hydrogen bubble char Jer and to the c o n s t r u c t o r s of t h e R F s e p a r a t e d b e a m . W e w o u l d like to thank the scanning, measuring and computi n g s t a f f s a t e a c h of o u r L a b o r a t o r i e s . W e a r e p l e a s e d to a c k n o w l e d g e h e l p f u l d i s c u s s i o n s w i t h D r . R. A r m e n t e r o s a n d P r o f . Ch. P e y r o u .
References 1. P . B r a m h a m , R . D . F o r t u n e , E.Keil, H. Lengeler, B. W. Montague and W. W. Neale, P h y s i c s L e t t e r s 15 (1965) 290. 2. J . M . B i s h o p , A . T . Goshaw, A.R, Erwin, M . A . T h o m p . son, W. D. Walker and A. Weinberg, Phys. Rev. L e t t e r s 16 (1966) 1069.
PHYSICS
14. See, eg.: C.Alff, D. Berley, D. Colley, N.Gelfand, U. Nauenberg, D . M i l l e r , J. Schultz, J . S t e i n b e r g e r , T. H. Tan, H, B r u g g e r , P. K r a m e r and R. Plane, Phys. Rev. L e t t e r s 9 (1962) 325; B. Buschbeck-Czapp, I. Wacek, W.A. Cooper, A. F r i d m a n , E . M a l a m u d , G . O t t e r , E . G e l s e m a and A. T e n n e r , P r e c . of the Sienna Intern. Conf. on E l e m e n t a r y P a r t i c l e s (1963) 166; N. Gelfand, D . M i l l e r , M. Nussbaum, J. Ratau, J. Schultz, J. Steinberger, T.H. Tan, L. K i r s c h and R. Plane, Phys. Rev. L e t t e r s 11 (1963) 463; J. J. M u r r a y J r . , M. F e r r o _ L u z z i , D.O. Huwe, J. B. Schafer, F . T . Solmitz and M. Lynn Stevenson, P h y s i c s L e t t e r s 7 (1963) 358;
OBSERVATION
OF
LETTERS
R. Kraemer, L. Madansky, M. Meer. M. Nussbaum. A. Pevsner. C. Richardson, R.Strand. R. Zdnnis. T, Fields, S.Orenstein and T. Toohig, Phys. Rev. 136 (1964) B496; S . M . F l a t t e , D.O.Huwe, J . J . M u r r a y . J . B u t t o n Shafer, F . T . Solmitz, M. Lynn Stevenson and C. Wohl, Phys. Rev. L e t t e r s 14 (1965) 1095. 15. M. Gell-Mann, D. Sharp and W. G, Wagner, Phys. Rev. L e t t e r s 8 (1962) 261; W. E. T h i r r i n g , P h y i c s L e t t e r s 16 (1965) 335; C. Becchi and G. Morpurgo, Phys. Rev. 140 (1965) B687; S. K. Kundu, Phys. Rev. 141 (1966) 1529.
A (K~z) R E S O N A N C E
Aachen-Berlin-CERN-London
15 August 1966
NEAR
(I.C.)-Vienna
1800
MeV
Collaboration
J. BARTSCH, M. D E U T S C H M A N N , E. K E P P E L , G. K R A U S
and R. S P E T H Physikalisches Institut der Technischen Hochschule, Aachen, Germany C. G R O T E , J. K L U G O W , D. P O S E , H. S C H I L L E R and H. V O G T Forschungsstelle flit Physih Hoher Energien der Deutschen Akadernie der Wissenschaften zu Berlin, Zeuthen, Germany
M. BARDADIN-OTWINOWSKA *, V. T. C O C C O N I , P. F. D A L P I A Z **, E. F L A M I N I O * * * , J. D. H A N S E N ~, H. H R O M A D N I K ~ , G. K E L L N E R , D.R.O. MORRISON and S. N O W A K % ~ CERN, European Organization f o r Nuclear Research, Geneva N. C. B A R F O R D ,
D. P. D A L L M A N , S. J. G O L D S A C K , M.E. MERMIKIDES Physics Department, Imperial College, London
and N. C. M U K H E R J E E
A. F R O H L I C H , G. O T T E R , I.W A C E K and H. W A H L Institut f~r Theoretische Physik der Universit~it, Vienna Received 11 July 1966 Both in the reaction K-p --~pK-ff+~"- and in the reaction K-p --*pK°ff-Tt°induced by I0 GeV/c negative kaons on hydrogen, an enhancement is observed in the (Kffff)-effectivemass distribution, at mass M = 1789 • 10 M e V and with fullwidth at half height r = 80 +240 MeV. Evidence is presented which is consistentwith the interpretationof this enhancement as a resonk5~ state of isospin I = ½, with possible decay modes into Kp, K*ff and Zc0. It is proposed to name this resonance the L-meson.
A b o u t 200 000 p h o t o g r a p h s of 10 G e V / c n e g a t i v e k a o n s , w i t h a n a v e r a g e of 5 k a o n s / p i c t u r e , were taken at the CERN proton-synchrotron in t h e 150 c m B r i t i s h h y d r o g e n b u b b l e c h a m b e r . This was the first experiment performed with a h i g h e n e r g y r a d i o - f r e q u e n c y s e p a r a t e d b e a m [1]. The events with 2 and 4 prongs, whether or not a strange particle is seen to decay, were measured on IEP or similar machines and aria-
* ** *** t t?
On leave f r o m the University of Warsaw. CERN Fellow f r o m the University of Bologna. CERN Fellow f r o m the University of P i s a . CERN Fellow f r o m the U n i v e r s i t y of Copenhagen. CERN Fellow f r o m the Institut f u r T h e o r e t i s c h e Physik, Vienna. t~t On leave from the Forschungsstelle fur Physik Hoher Energien, Berlin-Zeuthen.
35'7
Volume 22, number 3
PHYSICS LETTERS
l y s e d with the T H R E S H - G R I N D - S L I C E - S U M X s y s t e m of p r o g r a m s . Out of ~9000 e v e n t s f o r which k i n e m a t i c f i t s w e r e obtained, 994 e v e n t s w e r e c l a s s i f i e d $ as belonging to the r e a c t i o n :
15 August 1966
R e a c t i o n s (1) and (2), t h e r e f o r e , p a r t l y p r o c e e d v i a f o r m a t i o n of the two-body i n t e r m e d i a t e state: K ' p -~ p L - .
K- p ~ pK-Tr+~ and 425 e v e n t s to the r e a c t i o n : K- p ~ pK°Tr'Tr ° .
(2)
Since in the r e a c t i o n (1) the p o s i t i v e pion f r e quently c o m b i n e s with the p r o t o n to f o r m the N*++(1238) i s o b a r , in the following a n a l y s i s of the (KTr~) s y s t e m only 699 e v e n t s of this r e a c t i o n have been used, f o r which no (pTr+) c o m b i n a t i o n is in the m a s s r e g i o n 1.12 to 1.34 GeV. In fig. l a and Ib a r e shown the (KTrTr)- e f f e c t i v e m a s s d i s t r i butions f o r r e a c t i o n (i), N*++ excluded, and f o r r e a c t i o n (2). The shaded a r e a s c o r r e s p o n d to the e v e n t s f o r which the s q u a r e f o u r - m o m e n t u m , It I, t r a n s f e r r e d to the proton, s a t i s f i e s the condition Itl < 0.6 (GeV/c) 2. In fig. Ic is shown the s u m of t h e s e d i s t r i b u t i o n s f o r It] < 0.6 (GeV/c) 2. It can be s e e n in the f i g u r e s that t h e r e is a b r o a d peak n e a r 1330 MeV and a n a r r o w e r peak n e a r 1800 MeV. The f i r s t peak m a y contain s e v e r a l of the e n h a n c e m e n t s r e p o r t e d in the l i t e r a t u r e *. In this l e t t e r we a r e c o n c e r n e d with the second peak which is o b s e r v e d h e r e f o r the first time. Since t h e r e e x i s t s at p r e s e n t no adequate m e a n s of c a l c u l a t i n g the shape of the n o n - r e s o nant b a c k g r o u n d in the d i s t r i b u t i o n of fig. l c , s e v e r a l " b a c k g r o u n d s " have been drawn by hand in the r e g i o n M ( I ~ ) > 1.50 GeV, and f i t s have been made to the e x p e r i m e n t a l d i s t r i b u t i o n in fig. l c with such background s h a p e s and with a B r e i t - W i g n e r c u r v e to d e s c r i b e the peak n e a r 1800 MeV. The f i t s i n d i c a t e that the (K~lr) e n h a n c e m e n t o c c u r s at a m a s s M = 1789 ~- l ~ / I e V , and has a full width at half height r = 80 _+~ MeV. The e r r o r s g i v en above contain a ll o w a n c e f o r the s y s t e m a t i c u n c e r t a i n t y d e r i v i n g f r o m the l a c k of knowledge of the t r u e background shape. The a s y m m e t r i c e r r o r in F d e r i v e s f r o m the f a c t that the e x p e r i m e n t a l r e s o l u t i o n is not m u c h s m a l l e r than the peak width i t s e l f **. In the m a s s r e g i o n of the e n h a n c e m e n t (1.71 to 1.87 GeV), the b a c k ground a c c o u n t s f o r 40 to 50%, depending on the b a c k g r o u n d ch o s en , of the e v e n t s o b s e r v e d , and the peak stands 5 to 7 s t a n d a r d d e v i a t i o n s above background. As our d a t a o f f er no o t h e r explanation of this e n h a n c e m e n t (e.g. r e f l e c t i o n o r o t h e r k i n e m a t i c effect), we a r e led to conclude that t h e r e e x i s t s a K~v r e s o n a n t state at this m a s s and p r o p o s e to n a m e it the L-meson.
358
(3)
(1) It may be noted that the r e s t r i c t i o n to s m a l l It ] does not a l t e r s u b s t a n t i a l l y the n u m b e r of e v e n t s i n t h e L - m e s o n r eg i o n . The c r o s s s e c t i o n f o r the p r o d u c t i o n of the L m e s o n in r e a c t i o n (3) is of the o r d e r of 100 ~b. The i s o s p i n of this r e s o n a n c e can be I = ½ or ~2. Some p o s s i b l e d e c a y m o d e s of the L - m e s o n a r e s u g g e s t e d by the d i s t r i b u t i o n s in fig. 2. Fig. 2a shows ~he 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 f o r the s y s t e m (K-w) as obtained f r o m the e v e n t s of r e a c t i o n : K - p ~pK-Tr+Tr-Tr ° ,
(4)
by excluding N*++(1238) and r e q u i r i n g that the t h r e e - p i o n s y s t e m be in the m a s s r e g i o n of the o m e g a - m e s o n (0.75 to 0.81 GeV). Fig. 2b shows the (Ky)- m a s s d i s t r i b u t i o n f o r the e v e n t s of the reactions: K ' p ~pK-Tr ° ,
(5)
K-p~p~°-
(6)
.
The d i s t r i b u t i o n in fig. 2c is obtained f o r the e v e n t s of r e a c t i o n s (1) and (2) by set t i n g the c o n ditions that the d i - p i o n s y s t e m s c o n s i d e r e d a r e t h o se with e f f e c t i v e m a s s in the r e g i o n of the r h o - m e s o n (0.62 to 0.88 GeV) and the d i s t r i b u t i o n in fig. 2d is s i m i l a r l y obtained by r e q u i r i n g that the (K~) s y s t e m s c o n s i d e r e d a r e t h o se with e f f e c t i v e m a s s in the r e g i o n of the K*(890) r e s o n a n c e (0.85 to 0.93 GeV). It can be s e e n that the d i s t r i b u t i o n s in fig. 2a, 2c and 2d all p r e s e n t e n h a n c e m e n t s at around 1300 MeV and 1800 MeV, while no e n h a n c e m e n t s at those m a s s e s a r e s e e n in fig. 2b, w h e r e , howe v e r , the r e s o n a n c e s K*(890) and K*(1400) stand out c l e a r l y . Thus, no e v i d e n c e is obtained f o r the d ecay L ~ Ky, while the r e s u l t s in fig. 2a m ay be c o n s i d e r e d as e v i d e n c e f o r the d ecay L - - Kw. In fact, in the m a s s r e g i o n of the L - m e s o n , 2 e v e n t s $ The fiducial region in which events of reaction (2) were studied is about twice as large as the region in which events of reaction (1) were taken. * For a summary of the references on (K~'y) resonances with mass of 1170, 1215, 1275, 1320 and 1400 MeV, see ref. 2. ** The experimental resolution in this experiment is of 40 MeV, as estimated from the fitted value of the full width at half height of the omega-peak observed in the effective mass distribution of the three-pion system in reaction K-p ~ pK- w+y-11° .
V o l u m e 22, n u m b e r 3
K-p
PHYSICS
INTERACTIONS
=)
15 A u g u s t 1966
AT 10 GeVIc
p K'e÷Tr" 4( --~
LETTERS
~ lo
O)
o
K ' P - - pK'u) - - PK'tf*ff'lle T
~
• It I
i
20
(Kw)" [FFEC'n~ MASS.
>ao NO b)
K p--,,pfl'K°oBs. PLUS • K ' p ~ prr K"
l
o :[
AT 1 0 ~ 1 ¢
N ~ + ÷ EXCLUDED 699 EVENTS
0
AT 10G~Ic 2
o
maT
~
Z
v
~
~
w> 2( LLI
iv.
Itl
o
u.I m
|K~o)-EFFECTNE MASS, GeV
Z
.
4c
.
.
.
d) ~ K-p~PK~-II'-"PK*lT-'w* I L~ PLUS [ ] KK~'-~ pK-n''n- (NON~'~')
1.0
(K1TTf)
2.0 EFF.
3.0
i
2
(l~W)- EFFECTNE MASS,GeV
MASS,GeV
F i g . 1. a) 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 of t h e ( K n z 0 - s y s t e m f o r e v e n t s of r e a c t i o n (1) f o r w h i c h t h e (pTr +) s y s t e m i s n o t in t h e m a s s r e g i o n of t h e N*. T h e s h a d e d a r e a c o r r e s p o n d s to t h e e v e n t s with I t I < 0.6 (GeV/c) 2. b) 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 of the (K~rn)- s y s t e m f o r the e v e n t s of r e a c t i o n (2). T h e s h a d e d a r e a c o r r e s p o n d s to the e v e n t s with I tl < 0.6 (GeV/c) 2. c) S u m of t h e two a b o v e d i s t r i b u t i o n s , f o r t h e e v e n t s in w h i c h t h e s q u a r e d f o u r m o m e n t u m t r a n s f e r r e d to t h e p r o t o n is I tl < 0.6 (GeV/c) 2.
F i g . 2. a) (Kc0)- 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 obtained f r o m r e a c t i o n (4). b) (KTr)- 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 o b t a i n e d f r o m r e a c t i o n s (5) and (6). c) ( K p ) - 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 o b t a i n e d f r o m r e a c t i o n s (1) and (2). d) ( K * ~ ) - 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 obtained f r o m r e a c t i o n s (1) and (2).
359
Volume 22, n u m b e r 3
PHYSICS
LETTERS
15 August 1966
Table 1 Expected values of the r a t i o s indicated, for isospin ½ and ~ of the L - m e s o n , and corresponding e x p e r i m e n t a l values deduced f r o m r e a c t i o n s (1) and (2). The expected values a r e calculated c o r r e c t i n g for unobservable decay modes, probability of detecting the K ° and difference in size of fiducial regions for r e a c t i o n s (1) and (2). Isospin of L-meson
K* -(S90)~"° --, (K°Tr-) ?To
K*O(890)~.- --, (K-~+)~.- + (KOy°)~"-
K*O(S90)y- --, (K°~.°) 7r-
K* -(890)7 ° -'~ (K°Tr-) ?r°
Theo r.
Expt.
Theor.
Expt.
1 2
0.9 + 0.6
a r e e x p e c t e d f r o m t h e b a c k g r o u n d , a n d 12 e v e n t s a r e o b s e r v e d . T h e e x i s t e n c e of t h e d e c a y L --* Kw w o u l d i m p l y t h a t t h e i s o s p i n of t h e L - m e s o n i s [=1~. T h e e n h a n c e m e n t s o b s e r v e d a t a r o u n d 1800 M e V i n t h e (Kp) a n d (K*~) m a s s d i s t r i b u t i o n d o not prove, but are consistent with the decays L ~ K p a n d L -~ K*~. If t h e a s s u m p t i o n i s m a d e t h a t t h e e n h a n c e m e n t s a t 1800 M e V o b s e r v e d i n t h e v a r i o u s c h a r g e s t a t e s of (K*~) m a s s d i s t r i b u t i o n s do r e p r e s e n t t h e d e c a y L ~ K*~, t h e n t h e d a t a c o n f i r m t h e a s s i g n m e n t I =~.1 T h i s i s s h o w n i n t a b l e 1, w h e r e t h e e x p e r i m e n t a l v a l u e s f o r t h e ratios indicated are given along with the values e x p e c t e d f o r I = ½ a n d I = ~. A K~ resonance cannot have spin and parity, JP = 0 +. If t h e d e c a y L ~ Ky r e a l l y d o e s n o t e x i s t , it may be that the L-meson has spin and parity incompatible with such a decay, i.e., that the Lm e s o n h a s JP i n t h e s e r i e s 0 - , 1 +, 2 - , . . .
360
3.0 :e 1.5
We are deeply indebted to the operating crews of t h e C E R N p r o t o n s y n c h r o t r o n , of t h e 150 c m British hydrogen bubble char Jer and to the c o n s t r u c t o r s of t h e R F s e p a r a t e d b e a m . W e w o u l d like to thank the scanning, measuring and computi n g s t a f f s a t e a c h of o u r L a b o r a t o r i e s . W e a r e p l e a s e d to a c k n o w l e d g e h e l p f u l d i s c u s s i o n s w i t h D r . R. A r m e n t e r o s a n d P r o f . Ch. P e y r o u .
References 1. P . B r a m h a m , R . D . F o r t u n e , E.Keil, H. Lengeler, B. W. Montague and W. W. Neale, P h y s i c s L e t t e r s 15 (1965) 290. 2. J . M . B i s h o p , A . T . Goshaw, A.R, Erwin, M . A . T h o m p . son, W. D. Walker and A. Weinberg, Phys. Rev. L e t t e r s 16 (1966) 1069.