Charmonium Results From BESIII
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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。
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