Study of Scalar Mesons at BES

Xiaoyan SHEN

Representing BES Collaboration

Institute of High Energy Physics, CAS

QWG3

Oct. 12 – 15, 2004, Beijing

Introduction

Light Scalar Mesons: , f0(980)

f0(1370)

f0(1500)

f0(1710), f0(1790)

Summary

Outline

0

10

20

30

40

50

60

CBAL MK II MK III DM2 BES I BES II

BESII Detector

VC: xy = 100 m TOF: T = 180 psMDC: 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

Introduction

0

2

4

6

8

10

12

14

MKI MKII MKIII CBAL BESI BESII CLEOc

J/

(2S)

World J/ and (2S) Samples (×106) BESII

58M J/

BESII 14M (2S)

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

M()M(+-0)

M(+-)

0

Breit-Wigner for :

Fit to J/→+ (whole mass region)

f0 contribution

preliminary

b1(1235)Method I:

Channels fitted to the data:

J/f2(1270) f0(980) b1(1235) ’(1450) f2(1565) f2(2240)

f2 contribution

Fit to J/→+ (M < 1.5 GeV)

Method II:

Channels fitted to the data:

J/f2(1270) f0(980) b1(1235) phase space

f0 contribution

f2 contribution

Fit results:

Averaged pole position:

(541 39) (252 42)i MeV

P. L. B 598 (2004) 149-158

Method I

Method II

K*(892)K0*(1430), K2*(1430) K1(1270), K1(1400)

ρ(770)

BES Preliminary

κ

K*0(1430)

BES Preliminary

κ

Study of f0(980), f0(1370), f0(1500), f0(1710) and f0(1790) from:

KK

KK

KKJ

,

,

,/

Important parameters from PWA fit:

Large coupling with KK indicates big component in f0(980)

/J

KKJ /

f0(980) at BES

21.025.021.4

1510165

68965

g

g

MeVg

MeVM

KK

ss

f0(980)

f0(980)BES II P

reliminary

There has been some debate whether f0(1370) exists or not.

f0(1370) clearly seen in

J/ , but not seen in J/ .

/J

/J

PWA 0++ components

f0(1370)

NO f0(1370)

f0(1370) at BES

MeV

MeVM

40265

501350

BES II Prelim

inary

Clear f0(1710) peak in J/ KK.

No f0(1710) observed in J/ !

f0(1710) at BES

KKJ /

/J

f0(1710)

NO f0(1710)

MeV

MeVM

20125

301740

CLKKfBR

fBR%95@13.0

))1710((

))1710((

0

0

BES II Prelim

inary

A clear peak around 1790 MeV is observed in J/ .

No evident peak in J/ KK. If f0(1790) were the same as f0(1710), we would have:

Inconsistent with what we observed in J/ , KK

New f0(1790) at BES ??

BES II Prelim

inary

/Jf0(1790)

KKJ /

?

MeV

MeVM6030

4030

270

1790

5.1~))1710((

))1790((

0

0

KKfBR

fBR

CLKKfBR

fBR%95@13.0

))1710((

))1710((

0

0

Is f0(1790) a new scalar ??

Scalars in J/ , KK

Two scalars in J/ :

One is around 1470 MeV, => f0(1500)

The other is around 1765 MeV, is it f0(1790) or f0(1710) or a mixture of f0(1710) and f0(1790)?

/J?)1500(0f ?)1710(0f

00/ J

BES II Prelim

inary

KKJ /

00/ ss KKJ

)1710(0f

)1710(0f

PWA analysis showsone scalar.

MeV 166

MeV 41740155108

1025

M

Phys. Rev. D 68 (2003) 052003

BES Preliminary

BES Preliminary

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 deter

mines the or component, respe

ctively. OZI rule

dduu ss

/J /J

dduu

ss

Unusual properties of f0(1370), f0(1710) and f0(1790)

f0(1710): It dominantly decays to KK (not to ) It is mainly produced together with (not ) What is it ?

f0(1370) and f0(1790) They dominantly decays to (not to KK) It is mainly produced together with (not ) What are they ?

Scalar Puzzle – no good answer yet!

dduu

dduu

ss

ss

Summay

pole obtained in J/ pole in J/K*K and KK the parameters of f0(980) are determined scalar puzzle? Further study needed.