QCHS 2010 Lei Zhang 1 Lei Zhang ([email protected] ) (on behalf of BESIII Collaboration) Physics School of Nanjing University Recent Results of ’ decays at BESIII QCHS-IX 2010, Aug. 30th–Sep. 3th , 2010, Madrid, Spain
Jan 08, 2016
QCHS 2010 Lei Zhang 1
Lei Zhang([email protected])
(on behalf of BESIII Collaboration)
Physics School of Nanjing University
Recent Results of ’ decays at BESIII
QCHS-IX 2010, Aug. 30th–Sep. 3th , 2010, Madrid, Spain
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Outline: Studies of hc
E1-tagged analysis of ’ 0 hc, hc c
Inclusive analysis of ’ 0 hc
Two photon transition: ’ J
Measurement of ’γπ0, γη and γη’Performance of BESIII
EMCVery important
BESIII detector
Use time information to reject beam gas
Add energy deposit in TOF
Improve detection : veto backgrounds and add TOF energy
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in’c2
Compare MC with data in ’ c1 in’ J
efficiency
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hc :What’s it? What do we know?Spin singlet P wave (L=1, S=0) charmonium state potential model spin-spin-interaction tells us:
Before BESIII
Non-zero spin-spin interaction
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E1-tagged ’hc, hcc
N(hc)= 3679±319
M(hc)=3525.40±0.13±0.18MeV
(hc) = 0.73±0.45±0.28MeV
< 1.44MeV@90%CL
Consistent with CLEO:
3525.35±0.19±0.11MeV
and theoretical prediction.
First measurement
Method: ’0hc , hc c
Inclusive analysis of ’ 0 hc (requiring a soft )
E1-tagged analysis of hc c (requiring a )
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Inclusive ’hc
Br(’ 0 hc) x Br(hc c) =(4.58±0.40±0.50) ×10-4
consistent with CLEO:(4.22±0.44±0.52) ×10-4
N(hc) = 10353±1097
Br(’ 0hc) = (8.4±1.3±1.0) ×10-4 Br(hc c) = (54.3±6.7±5.2)%
First measurement
Method: Only requiring a soft
BESIII Collaboration, PRL 104, 132002 (2010)
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Short summary of hc
First Measurement!
(1) Kuang, PRD65, 094042 (2002)(2) Godfrey, Rosner, PRD66, 014012 (2002)
Consistent with CLEO
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Theoretical study is on going. (Z.G. He et al)
’J/two photons transition
Potential model :• Discrete part:
double E1 transition via discrete χCJ (nP) (n=1,2) states (virtual and real parts). (including main source of the background)(well described χCJ states)
• Relativistic correction:Higher order v2 operators corrections
naive theoretical pictures :
Potential model + couple channel:• Besides discrete contribution, the
hadron-loop effect also may play an important role.
2010-6-10
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Scattering Plot: Mγγ VS Mγ2 recoiled
box cut:
channelCJ
e+e- channel
γ1 : high energy photon
γ2 : low energy photon
0.15 < Mγγ < 0.51 GeV
3.43 < Mγ2 rec. < 3.49 GeV
Analysis of ’J/J/e+e-/
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Di-lepton Invariant Mass
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Known backgrounds:
• QCD background from ’ decay
• QED background from continuum data
Significant enhancement around J/ψ peak
]GeV/c[ 2llM ]GeV/c[ 2
llM
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Preliminary Numerical Results
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Simulation of physics mechanism of signal process under study and not included here
Possible signal-CJ-decay interference not included
Branching Fractions of ’ γP(π0, η, η')
• In the limit of OZI rule and SU(3) flavor symmetry, the charmonium radiative decay obey:
(θp is pseudo-scalar mixing angle, p is momentum of η' or η in the center of mass
system). This formula predicts R1 ≈R2.
• The recent CLEO result: – R1 = (21.1±0.9)% but R2<1.8% @ 90% C.L.
• Ψ’→γπ0 can be described by the vector dominant model(VDM), but the experiment has not been able to fix the theory for the large experimental uncertainty.
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General Event Selection
• Photons selection: – Geometrical Acceptance
– Energy Threshold
• Charged tracks selection:– Primary Vertex
• Intermediate Meson Mass
Reconstructed channels
The key background suppression in ’γπ0 channel
Deadly background:
γ conversion in e-e+ → 2γ process in outer MDC.
Method:
MDC hits are counted in corresponding sector to suppress this background
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Invariant mass spectra
• Unbinned maximum likelihood fit
• Left backgrounds: QED (blue dashed line)
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abcde
Ns: signal yieldNc: continuum BKGNr: expected ’ BKGε: Monte-Carlo efficiency
Numerical results
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The significances of Ψ’ →γπ0 and Ψ’→γη are 4.1 and 3.1 σ standard deviation respectively.
R2 = (1.01±0.37±0.07) % which is not expected by any theoretical models.
(10-6)
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Several charmonium decays investigate based on 106M ’ data at BESIII
Observation of hc from ’ 0hc
First measurement: Br(’ 0hc) & Br(hcc) separately, as well as the width of hc
Mass of hc and Br(’0 hc) X Br(hcc) is consistent with CLEOc’s results
A significant enhancement of two-photon transition of ψ’ to J/ψ observed for the first time : significance>10 σ. The branching ratio determined by two independent channels to be
First evidence for ’γπ0, γη with 4.1 and 3.1 σ standard deviation respectively, and R2 = (1.01±0.37±0.07) %.
More exciting results, which will improve our knowledge at this energy region, are coming soon.
Summary
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Thank you!
谢谢!