Study of Scalar Mesons at BES
Xiaoyan SHEN
Representing BES Collaboration
Institute of High Energy Physics, CAS
QWG3
Oct. 12 – 15, 2004, Beijing
Outline

Introduction

Light Scalar Mesons:
, 
f0(980)
f0(1370)
f0(1500)
f0(1710), f0(1790)

Summary
Introduction
BESII Detector
World J/ and (2S) Samples
(×106)
BESII
58M J/
60
50
J/
40
30
20
10
0
VC: xy = 100 m
TOF: T = 180 ps
MDC: xy = 220 m
BSC: E/E= 21 %
dE/dx= 8.5 %
 = 7.9 mr
p/p=1.78(1+p2)
z = 2.3 cm
 counter: r= 3 cm
B field: 0.4 T
z = 5.5 cm
CBAL
MKII
MKIII
DM2
BESI
BESII
BESII
14M (2S)
14
12
(2S)
10
8
6
4
2
0
MKI
MKII
MKIII
CBAL
BESI
BESII CLEOc
Light Scalar Mesons:
σ, κ, f0(980), f0(1370),
f0(1500), f0(1710), f0(1790)
Why are light scalar mesons interesting?

There have been hot debates on the existence of
 and  .

Lattice QCD predicts the 0++ scalar glueball
mass from 1.5 - 1.7 GeV. f0(1500) and f0(1710)
are good candidates.
 f0(1370), f0(1500), f0(1710)
were found in the fixed
target, ppbar, e+e- experiments. The confirmation
of them is important.
The  pole in J /    
0
M()

M(+-)
M(+-0)


Breit-Wigner for :
Fit to J/→+ (whole mass region)
Method I:
b1(1235)
Channels fitted to
the data:
J/f2(1270)

f0(980)
b1(1235)
’(1450)
f2(1565)
f2(2240)
preliminary
f2 contribution
f0 contribution
Fit to J/→+ (M < 1.5 GeV)
f2 contribution
Method II:
Channels fitted to
the data:
J/f2(1270)

f0(980)
b1(1235)
phase space
f0 contribution
Fit results:
Method I
Method II
Averaged pole position:
(541  39)  i (252  42) MeV
P. L. B 598 (2004) 149-158
ρ(770)
K*(892)
K0*(1430), K2*(1430)
K1(1270), K1(1400)
K*0(1430)
κ
κ
Study of f0(980), f0(1370), f0(1500),
f0(1710) and f0(1790) from:
J /   , KK
  , KK
  , KK
f0(980) at BES

J /   


f0(980)
Important parameters from
PWA fit:
M  965  8  6 MeV
g  165  10  15 MeV
g KK
 4.21  0.25  0.21
g
J /  K K


f0(980)

Large coupling with KK
indicates big ss
component in f0(980)
f0(1370) at BES
J /    
J /    
PWA 0++ components

There has been some
debate whether f0(1370)
exists or not.

f0(1370) clearly seen in
J/  , but not seen in
J/  .
f0(1370)
NO f0(1370)
M  1350  50 MeV
  265  40 MeV
f0(1710) at BES

J /  K  K 
f0(1710)
Clear f0(1710) peak in
J/  KK.
M  1740  30 MeV
  125  20 MeV

J /    
NO f0(1710)
No f0(1710) observed in
J/   !
BR ( f 0 (1710)   )
 0.13 @ 95%CL
BR ( f 0 (1710)  KK )
New f0(1790) at BES ??

A clear peak around 1790 MeV
is observed in J/  .
M  179040
30 MeV
J /    
60
  27030
MeV
f0(1790)

No evident peak in J/  KK.
If f0(1790) were the same as
f0(1710), we would have:
BR ( f 0 (1790)   )
~ 1.5
BR ( f 0 (1710)  KK )
?
J /  K  K 
Inconsistent with what we
observed in J/   , KK
BR ( f 0 (1710)   )
 0.13 @ 95%CL
BR ( f 0 (1710)  KK )
 Is f0(1790) a new scalar ??
Scalars in J/  , KK
J /    
f 0 (1500) ?
Two scalars in J/  :
f 0 (1710) ?
 One
is around 1470 MeV,
=> f0(1500)
 The
J /   0 0
other is around 1765
MeV, is it f0(1790) or
f0(1710) or a mixture of
f0(1710) and f0(1790)?
J /  K  K 
f 0 (1710)
PWA analysis shows
one scalar.
M  1740  4 10
25 MeV
J /  K s0 K s0 f (1710)
0
15
  1668510
MeV
Phys. Rev. D 68 (2003) 052003
f0(1500) at BES

One scalar with a mass = 1466  6  16 MeV
is needed in J/ .
f0(1500).

No peak directly seen in , KK, , KK.
OZI rule and flavor tagging
in J/ hadronic decays

In J/ hadronic decays, an  or  signal
determines the uu  dd or ss component,
respectively.  OZI rule


J /
J /
uu  dd
ss
Unusual properties of
f0(1370), f0(1710) and f0(1790)
 f0(1710):
 It
dominantly decays to KK (not to ) 
ss
is mainly produced together with  (not )  uu  dd
 What is it ?
 It
 f0(1370)
 They
 It
and f0(1790)
dominantly decays to  (not to KK)  uu  dd
is mainly produced together with  (not ) 
 What
ss
are they ?
 Scalar Puzzle – no good answer yet!
Summay
 pole obtained in J/
  pole in J/K*K and KK
 the parameters of f0(980) are determined
 scalar puzzle? Further study needed.
