QCHS 2010 Lei Zhang 1

Lei Zhang(leizhang@ihep.ac.cn)

(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！