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Charmonium Results From BESIII

张景芝高能物理研究所

2010.04.19

南昌高能物理会议

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Charmonium Study @BES

• Spin singlet states are less known– hc

see Bian J.M.’s talk

– cc(2S)

not in this talk

• P wave spin triplet states cJ

this talk

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Why cJ

– Only a small part of decay modes are found (13% ,39%,26%)

– To understand the P-wave charmonium decay dynamic, and light hadron spectroscopy.

– Test QCD based theory at cJ hadronic decays

– The e+e- machine provides LARGE CLEAN sample via ’cJ

Leading-order QCD Color octect theory

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Are they small ??

cJ→VV (V=)• The past results

• c1VV are suppressed by Helicity Selection Rule (HSR)• c1 S wave forbidden, only allowed for L=2. • cJ OZI doubly suppressed.

cJ→ 00, • Interesting Channels for glueball searches

×10-3

c0 0.940.21 0.13

2.290.58 0.41

DOZI (Thy 0.45)

c2 1.700.30 0.25

1.770.470.36

DOZI (Thy 0.24)

c1 --

HSR

--

HSR

--

DOZI HSR

Ref: PLB630:7, 2005. PLB642:197,2006. PRD72,074001.Q.Zhao

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BESIII @ BEPC IIBESIII @ BEPC IIRFRF SR

IP

MDC: (pT)/pT=0.32%0.37% at 1GeV(dE/dx) = 5.8%

TOF: 90 ps (for bhabha)

EMC: (E)/E=2.5% at 1GeV (22% at BESII)

Beam energy: 1.0-2 .3GeVDesign peak luminosity: 1×1033 cm-2s-1 (100 BESII)Optimum energy: 1.89 GeV

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BESIII Data-taking

• July 19, 2008: First e+e-

collision event in BESIII• Achieved: 0.32×1033 cm-2s-1

Data samples:

’ events (150pb-1 )

42pb-1 at 3.65GeV

220M J/ events (65pb-1)

pb-1

Results presented are based on 106M ’

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EM transition inclusive photon spectrum

c2 c1

co

c1,2 J/

c

BESIII preliminary

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c0,2→ 00, 0 →

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Event selection

• No charged tracks• Photon: MeV, timing

0 , – -0.06<M()-m0<0.04; -0.09<M()-m<0.06 GeV/c2

– Decay angle cos < 0.95;

• Events– Have two with a minimum

Decay angle is the polar angle of in 0 / rest frame

0 0

0

2 0 2 01 1 2 2

0

/ /

2 2

( / ) ( / ),

where P( / )=(M( )-m )/ .

7 / , 12 / .

P P

MeV c MeV c

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Good agreement of data & MC

Number of

ptr

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’ →cJcJ→00,

Unbinned maximum LH Fit

– Signal PDF determined from MC – 2nd polynomial is used for bkg

2S)00

Nc0 17443±167 Nc2 4516±80

2S)

Nc0 2132±60 Nc2 386±25

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Systematics

• The systematic uncertainties from– detection (1% per )– reconstruction (1% per )– Selection cuts– Signal/bkg shape, fit range– Trigger (0.1%)– Number of ’ (4%)

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Results

• Precision improved.• Results are consistent with CLEOc.

Published in Phys.Rev.D81:052005,2010.

Note: the third error are due to the branching fractions of ’→ cJ

BR (10-3) c0 c2

00 BESIII 3.23±0.03±0.23±0.14 0.88±0.02±0.06±0.04

CLEO-c 2.94±0.07±0.32±0.15 0.68±0.03±0.07±0.04

PDG08 2. 43±0.20 0.71±0.08

BESIII 3.44±0.10±0.24±0.13 0.65±0.04±0.05±0.03

CLEO-c 3.18±0.13±0.31±0.16 0.51±0.05±0.05±0.03

PDG08 2.4±0.4 <0.5

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cJV V

Note: c1VV: S-wave forbidden; HSR suppression

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Event selection

• Photons

– |cos|<0.93; MeV

• Charged tracks

– |Vz|<5cm, |Vr |<0.5cm, |cos|<0.8

• Events– Ncharged = 4; Q=0; Nshould

– Selection best by minimizing 4C – MKK – mGeV;M – mG

eV–

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E1 photon angular distribution

• MC: E1 transition assumed in 2S)cJ

dN/dcos∝cos2

c0 c1 cJ2

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Observation of cJ

sideband

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cJ(cont.)

M(KK)

M(KK) M(KK)M(KK)

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distribution

• Obtained from 106M ’ data• Contribution from non-resonance estimated from

sideband (as blue)

0c 1c

2cBESIII Preliminary

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Observation of cJ

Non-resonance & other backgrounds are investigated from sideband.

()GeV

GeV

M(

) G

eV

M() GeV

sideband (0.9-1.2)

BESIII preliminary

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Observation of cJ

0

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Distribution of M(

• Background studied from sideband & 100M MC.

• Clear signal c0(K+K-) seen.

0c

1c2c

BESIII preliminary

M()

DOZI suppression

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Summary of cJ VV

• We are finalizing this analysis.

c0 Observ.

Observ. 1st Observ.

DOZI

c2 Observ. Observ.

DOZI

c11st Observ.

HSR

1st Observ.

HSR DOZI HSR

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总结

• BESIII 从 2008 开始取数据， 采集了 106M ’ 和 220M J/ 。

• 验证 MC 模拟和实验数据相符。• 利用 110M ’ 观测到了 cJ , cJ

及 c1 是首次发现。• BESIII 提高了 cJ 到双中性 赝标量介子对 分支比的测量，

包括 c0,2 ， c0,2.

• 大量分析工作正在进行中， BESIII 预期更多新结果。