scalar and pseudoscalar mesons at besii xiaoyan shen (representing bes collaboration) institute of...

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!