QCHS 2010 Lei Zhang1 Lei Zhang (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

QCHS 2010 Lei Zhang2 Outline: Studies of h c E1-tagged analysis of  ’   0 h c, h c    c Inclusive analysis of  ’   0 h c Two photon transition:  ’  J  Measurement of  ’  γπ 0, γη and γη ’ Performance of BESIII EMC Very important

BESIII detector Use time information to reject beam gas Add energy deposit in TOF Improve detection : veto backgrounds and add TOF energy QCHS 2010 Lei Zhang3

4  in  ’  c2 Compare MC with data  in  ’   c1    in  ’      J     efficiency

QCHS 2010 Lei Zhang5 h c :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

6 E1-tagged  ’   h c, h c  c N(h c )= 3679±319 M(h c )= ±0.13 ±0.18 MeV  (h c ) = 0.73±0.45 ±0.28 MeV < Consistent with CLEO: ±0.19±0.11MeV and theoretical prediction. First measurement Method:  ’  0 h c, h c  c Inclusive analysis of  ’   0 h c (requiring a soft   ) E1-tagged analysis of h c    c (requiring a  ) QCHS 2010 Lei Zhang

7 Inclusive  ’   h c Br(  ’   0 h c ) x Br(h c   c ) =(4.58±0.40±0.50) ×10 -4 consistent with CLEO: (4.22±0.44±0.52) ×10 -4 N(h c ) = 10353±1097 Br(  ’   0 h c ) = (8.4±1.3±1.0) ×10 -4 Br(h c    c ) = (54.3±6.7±5.2)% First measurement Method: Only requiring a soft   BESIII Collaboration, PRL 104, (2010)

QCHS 2010 Lei Zhang8 Short summary of h c First Measurement! (1) Kuang, PRD65, (2002) (2) Godfrey, Rosner, PRD66, (2002)  Consistent with CLEO

QCHS 2010 Lei Zhang99 Theoretical study is on going. (Z.G. He et al)  ’  J/  two photons transition Potential model : Discrete part: double E1 transition via discrete χ CJ (nP) (n=1,2) states (virtual and real parts). (including main source of the background) (well described χ CJ states) Relativistic correction: Higher order v 2 operators corrections naive theoretical pictures : Potential model + couple channel: Besides discrete contribution, the hadron-loop effect also may play an important role

QCHS 2010 Lei Zhang10 Scattering Plot: M γγ VS M γ2 recoiled box cut:     channel  CJ   e + e - channel γ 1 : high energy photon γ 2 : low energy photon 0.15 < M γγ < 0.51 GeV 3.43 < M γ2 rec. < 3.49 GeV Analysis of  ’  J/  J/  e + e - /    

QCHS 2010 Lei Zhang11 Di-lepton Invariant Mass 11 Known backgrounds: QCD background from  ’ decay QED background from continuum data Significant enhancement around J/ψ peak

QCHS 2010 Lei Zhang12 Preliminary Numerical Results Simulation of physics mechanism of signal process under study and not included here Possible signal-  CJ -decay interference not included

Branching Fractions of  ’  γP( π 0, η, η') In the limit of OZI rule and SU(3) flavor symmetry, the charmonium radiative decay obey: (θ p is pseudo-scalar mixing angle, p is momentum of η' or η in the center of mass system). This formula predicts R 1 ≈R 2. The recent CLEO result: –R 1 = (21.1±0.9)% but R 2 <1.8% ＠ 90% C.L. Ψ ’ →γπ 0 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. 13

14 General Event Selection Photons selection: –Geometrical Acceptance –Energy Threshold Charged tracks selection: –Primary Vertex Intermediate Meson Mass Reconstructed channels

The key background suppression in  ’  γπ 0 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 QCHS 2010 Lei Zhang15

Invariant mass spectra Unbinned maximum likelihood fit Left backgrounds: QED (blue dashed line) QCHS 2010 Lei Zhang16 abcdeabcde N s : signal yield N c : continuum BKG N r : expected  ’ BKG ε: Monte-Carlo efficiency

Numerical results QCHS 2010 Lei Zhang17 The significances of Ψ’ →γπ 0 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 )

QCHS 2010 Lei Zhang18  Several charmonium decays investigate based on 106M  ’ data at BESIII Observation of h c from  ’   0 h c First measurement: Br(  ’   0 h c ) & Br(h c  c ) separately, as well as the width of h c Mass of h c and Br(  ’  0 h c ) X Br(h c  c ) 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  ’  γπ 0, 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

QCHS 2010 Lei Zhang19 Gracias ！ Thank you! 谢谢！