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Lei Zhang ( leizhang@ihep.ac ) (on behalf of BESIII Collaboration)

Recent Results of y ’ decays at BESIII. Lei Zhang ( leizhang@ihep.ac.cn ) (on behalf of BESIII Collaboration) Physics School of Nanjing University. QCHS-IX 2010, Aug. 30th–Sep. 3th , 2010, Madrid, Spain. Outline: Studies of h c E1-tagged analysis of  ’   0 h c , h c    c

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Lei Zhang ( leizhang@ihep.ac ) (on behalf of BESIII Collaboration)

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  1. Recent Results of y’ decays at BESIII Lei Zhang (leizhang@ihep.ac.cn) (on behalf of BESIII Collaboration) Physics School of Nanjing University QCHS-IX 2010, Aug. 30th–Sep. 3th , 2010, Madrid, Spain QCHS 2010 Lei Zhang

  2. Outline: • Studies of hc • E1-tagged analysis of ’ 0 hc, hcc • Inclusive analysis of ’0 hc • Two photon transition: y’  ggJ/y • Measurement of y’γπ0, γη and γη’ Performance of BESIII EMC Very important QCHS 2010 Lei Zhang

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

  4. Compare MC with data g in y’gcc2 g in y’  gcc1 p0in y’  p0p0J/y p0efficiency QCHS 2010 Lei Zhang

  5. Before BESIII 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: Non-zero spin-spin interaction QCHS 2010 Lei Zhang

  6. E1-tagged y’p0hc, hcghc • Method: • y’p0hc , hc ghc • Inclusive analysis of ’0 hc (requiring a soft p0) • E1-tagged analysis of hcc (requiring a ) N(hc)= 3679±319 M(hc)=3525.40±0.13±0.18MeV G(hc) = 0.73±0.45±0.28MeV < 1.44MeV@90%CL First measurement Consistent with CLEO: 3525.35±0.19±0.11MeV and theoretical prediction. QCHS 2010 Lei Zhang

  7. Inclusive y’p0hc • Method: • Only requiring a soft p0 First measurement N(hc) = 10353±1097 Br(’  0hc) = (8.4±1.3±1.0) ×10-4 Br(hcc) = (54.3±6.7±5.2)% 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 BESIII Collaboration, PRL 104, 132002 (2010) QCHS 2010 Lei Zhang

  8. Short summary of hc Consistent with CLEO First Measurement! (1) Kuang, PRD65, 094042 (2002) (2) Godfrey, Rosner, PRD66, 014012 (2002) QCHS 2010 Lei Zhang

  9. y’ggJ/y: two photons transition naive theoretical pictures: • 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 • Potential model + couple channel: • Besides discrete contribution, the hadron-loop effect also may play an important role. Theoretical study is on going. (Z.G. He et al) 2010-6-10 QCHS 2010 Lei Zhang 9

  10. Analysis of y’ggJ/y, J/ye+e-/ m+m- Scattering Plot: Mγγ VS Mγ2 recoiled e+e- channel m+m- channel cCJ h p0 box cut: γ1 : high energy photon γ2 : low energy photon • 0.15 < Mγγ < 0.51 GeV • 3.43 < Mγ2 rec. < 3.49 GeV QCHS 2010 Lei Zhang

  11. Di-lepton Invariant Mass BESIII preliminary BESIII preliminary • Known backgrounds: • QCD background from y’ decay • QED background from continuum data Significant enhancementaround J/ψ peak 11 2010-6-10 QCHS 2010 Lei Zhang 11

  12. Preliminary Numerical Results • Simulation of physics mechanism of signalprocess under study and not included here • Possible signal-cCJ-decay interference not included 12 2010-6-10 QCHS 2010 Lei Zhang 12

  13. Branching Fractions of y’ 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 recentCLEO 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.

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

  15. The key background suppression in y’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 BESIII preliminary BESIII preliminary BESIII preliminary BESIII preliminary QCHS 2010 Lei Zhang

  16. Invariant mass spectra • Unbinned maximum likelihood fit • Left backgrounds: QED (blue dashed line) BESIII preliminary BESIII preliminary BESIII preliminary BESIII preliminary a b c d e BESIII preliminary BESIII preliminary Ns: signal yield Nc: continuum BKG Nr: expected y’ BKG ε: Monte-Carlo efficiency QCHS 2010 Lei Zhang

  17. Numerical results (10-6) BESIII preliminary • The significances of Ψ’ →γπ0 andΨ’→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. QCHS 2010 Lei Zhang

  18. Summary • Several charmonium decays investigate based on 106M ’ data at BESIII • Observation of hc from ’ 0hc • First measurement: Br(’ 0hc) & Br(hcc) separately, as well as the width of hc • Mass of hc and Br(’p0 hc) X Br(hc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 y’γπ0, γη with 4.1and 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. QCHS 2010 Lei Zhang

  19. Thank you! Gracias！ 谢谢！ QCHS 2010 Lei Zhang

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