Scalar and pseudoscalar mesons at BESIIXiaoyan SHEN

(Representing BES Collaboration)Institute of High Energy Physics, CAS, China

Charm06, June 5-7, 2006, IHEP, Beijing

Scalars: , , f0(980), f0(1370), f0(1500), f0(1710), f0(1790) …

PWA of J/

The threshold enhancement in J/

Study of J/

Focus on following results:

light scalars: ， , f0(980), f0(1370),

f0(1500), f0(1710), f0(1790)

Why light scalar mesons are interesting? There have been hot debates on the existence

of and . Lattice QCD predicts the lightest 0++ scalar glu

eball mass ~ 1.6 GeV. f0(1500) and f0(1710) are good candidates.

study in

study in

study f0(980), f0(1370), f0(1500), f0(1710) and f0(1790) in

/J

KKKKJ and / *

, / KKJ ，，

0++

The pole in at BESII

/J

M()

M(+-0)

M(+-

)

0

Averaged pole position: (541 39) (252 42)i MeV

Phys. Lett. B 598 (2004) 149

κ

24872

8173 MeV/c )45309()30841(

i

Phys. Lett. B 633 (2006) 681

Important parameters from PWA fit:

Large coupling with KK

/J

KKJ /

f0(980)

21.025.021.4

151016568965

gg

MeVgMeVM

KK

f0(980)

f0(980)

Phys. Lett. B 607 (2005) 243

There has been 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)

MeVMeVM

40265501350

Phys. Lett. B 607 (2005) 243

Clear f0(1710) peak in J/ KK.

No f0(1710) observed in J/ !

f0(1710) KKJ /

/J

f0(1710)

NO f0(1710)

MeVMeVM

20125301740

CLKKfBR

fBR %95@13.0))1710(())1710((

0

0

Phys. Lett. B 603 (2004) 138

KKJ /

00/ ss KKJ

)1710(0f

)1710(0fMeV 166

MeV 41740155108

1025

M

PWA analysis shows one scalar in 1.7 GeV region

Phys. Rev. D 68 (2003) 052003

f0(1710)

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)??

/Jf0(1790)

KKJ /

?

MeV

MeVM6030

4030

270

1790

5.1~))1710(())1790((

0

0

KKfBRfBR

CLKKfBR

fBR %95@13.0))1710(())1710((

0

0

f0(1790) is a new scalar ??

For global fit, the channels fitted in PWA

fix the parameters of f2(1810),f0(2020),

f2(2150) and f4(2050) to PDG values.

PWA results

Lower 0++ : 0++ is strongly preferred over 2++

f0(1370) cannot be excluded. f0(1710) or f0(1790) or both

If interpreting the 0++ in 1.75 GeV mass region as coming from f0(1710)

21411-

2

MeV/c 21108

MeV/c 2061466

M

215 510- 8-

21025

MeV/c 166

MeV/c 41740

M

?)1500(0f )2020(0f?)1710(0f

)1270(2f )1810(2f )2150(2f

)2050(4f all 0++ all 2++

PWA components: BES II Preliminary

vary the masses and widths within the errors add small components background level replace f2(1810) with f2(1950) J/ total number, tracking efficiency, kinematic fit, photon detection ……

For systematic errors:

BES II Preliminary

/J

00/ J

hep-ex/0603048

Observation of threshold enhancement in J/

) ,( 0 KK

OZI DOZI KKJ ,/ /J

M(+-0)

M(K

+K-

)

M(K+K-)

MeVMMKK

15||

MeVMMMeVKK

35||20

M(+-0)

Dalitz plot

Clear and signals

M2()

M2 (

)

A clear threshold enhancement is observed

Eff. curve

Phase Space

Side-bands

Side-bands do not have mass threshold enhancement!

Partial Wave Analysis of J/ X, X

The amplitudes are constructed with the covariant helicity coupling amplitude method. X is parameterized by a constant width BW. BG is approximated by non-interfering phase space. The decay information is not considered.

Best fit gives:JPC (X) = 0++, with S-wave X and systems.

Tried many alternative fits. The 2++ gives not bad likelihood value, but with more free parameters

0++ is favored over 0-+ and 2++

For systematic errors:

• uncertainty of the BG (different treatment,..)• fitting procedure (MC input and output) • MC eff., total number…

The DOZI decay of J/ is observed and measured with 58M J/ data. An enhancement in is found near the threshold. PWA shows: the enhancement favors 0++

.

Is it the same 0++ observed in KK or , or is it a glueball, or a hybrid …..?

2

21926

MeV/c 2820105

MeV/c 181812

M

Further look in , K*K*, …. is desirable !

410)65.027.061.2()()/( XBrXJBr

Phys. Rev. Lett., 96 (2006) 162002

0

/

J

M(+-0)(GeV/c2) M(+-0)(GeV/c2) M(+-0)(GeV/c2)

M(

+ -

0 )(G

eV/c

2 )

sideband

BES II Preliminary

signal after best candidate selection (best masses)

signal with multiple entries

Eff. curvePhase Space

Side-band

M()

Analysis of the angular distribution

for the system of 2 vector mesons:

spineven 0spin odd 0

)2cos(1/

ddN

signal region sideband

2sin/ ,1for ddN

JP = even- is dominant in system!

(1760) f0(1710)f0(1790)f0(1810)

PWA analysis

M()

Total

f2(1910) f2(160) BGUsing observed mass and width for f0(1810)in J/

f0(1710)

f2(1910) 5.8

f2(1640) 5.5

BG

(1760) > 10

f0 6.5

M() (GeV/c2)

dominated by (1760) a 0++ is possible needed (6.5 )

Accepted by PRD, hep-ex/06040453-

22421

2

100.32)0.08(1.98

))1760(())1760(/(MeV/c 25244

MeV/c 15101744

BrJBr

M

Summary and , f0(980), f0(1370), f0(1500), f0(1710), … are studied PWA of J/

the observation of threshold enhancement f0(1810) in J/

(1760) dominant in J/ , possible existence of f0 at around 1800 GeV.

Thanks!