Resent BES Results on Scalar Mesons

Zhipeng Zheng (Representing BES Collaboration)

Institute of High Energy Physics, CAS GHP-2004, Oct. 25

OUTLINE

Introduction and f0(980)

f0(1370), f0(1500), f0(1710) and f0(1790)

Summary

Introduction(1)

Why are light scalar mesons interesting?

The knowledge on the light scalars is very important to the understanding of QCD in nonperturbative region

There have been hot debates on the existence of and .

f0(980): precise parameters m, …. are needed.

Is it a state, or molecular or four quark state?

Lattice QCD predicts the 0++ scalar glueball mass from 1.5 - 1.7 GeV. f0(1500) and f0(1710) are good candidates.

Introduction(2)

ss KK

f0(1370), f0(1500), f0(1710) were found in the fixed target, , e+e- experiments. The confirmation of them is important.

f0(1500), f0(1710) are treated as mixed state of glueball with meson, but we need more information.

The BESII data have much higher statistics and lead to a much more decisive partial wave analysis.

Introduction(3)

pp

qq

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 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)

Introduction(4)

M() M(+-0)

M(+-)

0

The pole in J/+-

f2(1270)

f2(1270)

Fit Method I: (whole mass region)

f0 contribution

b1(1235)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)

Channels fitted to the data:

J/f2(1270) f0(980) b1(1235) P.S

f0 contribution

f2 contribution

Fit Method II: (M<1.5GeV)

Breit-Wigner for in the fit:

(1)(2)

(3)

(4)

Averaged pole position:

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

Method I

Method II

Fit Result

MeVi )42252()39541(

in J/K+ - K+ -

K0*(1430), K2*(1430)K*(892)

ρ(770)

K1(1270), K1(1400)

in J/K+ - K+ -

K*0(1430)K*

in KKJ */

f0(980) in J/+-,K+K-

Important parameters from PWA fit:

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

/J

KKJ /

21.025.021.4

1510165

68965

g

g

MeVg

MeVM

KK

ssf0(980)

f0(980)f0(1370)

f2(1525)

BESII preliminary

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

f0(1370) clearly seen in J/ , but not seen in J/ .

/J

/J

f0(1370)

NO f0(1370)

MeV

MeVM

40265

501350

f0(1370) in J/+-, +-

PWA 0++ components

f0(980)

f2(1270)

BESII preliminary

f0(1500) in J/+-, 00

/J

00/ J One scalar with a mass = 1466 6 16 MeV is needed in J / . It’s also needed in the fit of J / , kkNo peak directly seen in , KK, , KK channels.

f2(1270)

f2(1270)

f0(1500)

f0(1500)

f0(1500) f0(1710)

BESII preliminary

KKJ /

00/ ss KKJ

f0(1710) in

PWA analysis showsone scalar.

MeV166

MeV41740155

108

10

25

M

Phys. Rev. D 68 (2003) 052003

f0(1710)

f0(1710)

f2(1525)

f2(1525)

KKJ /

f0(1710) in J/ /J

00/ J

• The scalar around 1710MeV with mass

• Combine the branching ration of and kk, we

obtain:

MeV

MeVm

298145

111765 4

3

22.0

18.0

0

0 41.0))1710((

))1710((

KKfBR

fBR

f2(1270)

f0(1710)

f2(1270)

f0(1710)

BESII preliminary

f0(1710) in J/K+K-, +-

Clear f0(1710) peak in J/ KK.

No f0(1710) observed in J/ !

KKJ /

/J

f0(1710)

NO f0(1710)

MeV

MeVM

20125

301740

f2(1270)

PWA 0++ components

CLKKfBR

fBR%95@13.0

))1710((

))1710((

0

0

hep-ex/0409007

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!

/J

f0(1790)

KKJ /

?

MeV

MeVM6030

4030

270

1790

f0(1790) in J/K+K-, +-

f0(1710) 5.1~))1710((

))1790((

0

0

KKfBR

fBR

BESII preliminary

Summary of Scalar Meson at BES

Summary

Clear seen(peak + fit) in the fit

The existence of is confirmed in J/+ - with pole position:

Evidence for the as a peak close to threshold. Pole position:

Summary

MeVi )42252()39541(

MeVi )420~310()840~760(

f0(980) is clearly seen in both +-, K+ K- data, parameters of f0(980) are well determined.

Summary

21.025.021.4

1510165

68965

g

g

MeVg

MeVM

KK

f0(1370) is clearly seen in J/+- , But not evidence in J/+ -

f0(1500) is seen in J/ channel with mass:

f0(1710) is clearly seen in J/ KK with mass and width:

Summary

MeVM 1661466

MeV166

MeV,41740

155

108

10

25

M

f0(1710) is also seen in the J/, and K+K, but not seen in J/ +-

f0(1790) is needed in the fit of J/ +-, and need more study.

Summary