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Recent J/  Results from BESII

Recent J/  Results from BESII. Xiaoyan SHEN Representing BES Collaboration Institute of High Energy Physics, CAS Menu 2004 Aug. 29 – Sept. 4, 2004, Beijing. Outline. Introduction Multiquark candidates at BES * pp threshold enhancement in * p  threshold enhancement in

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Recent J/  Results from BESII

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  1. Recent J/ Results from BESII Xiaoyan SHEN Representing BES Collaboration Institute of High Energy Physics, CAS Menu 2004 Aug. 29 – Sept. 4, 2004, Beijing

  2. Outline • Introduction • Multiquark candidates at BES *pp threshold enhancement in * p threshold enhancement in * Kthreshold enhancement in • Study of the light scalar mesons • Study of the excited baryon states • Measurements of J/ and c decays • Search for LVF and search for pentaquark • Summary

  3. Introduction World J/ and (2S) Samples (×106) BESII Detector BESII 58MJ/ J/ BESII 14M(2S) • VC: xy = 100 m TOF: T = 180 ps • MDC: xy = 220 m BSC: E/E= 21 % • dE/dx= 8.5 %  = 7.9 mr • p/p=1.78(1+p2) z = 2.3 cm • counter: r= 3 cm B field: 0.4 T z = 5.5 cm (2S)

  4. Multi-quark candidates • Hadrons consist of 2 or 3 quarks： Naive Quark Model： • New forms of hadrons: • Multi-quark states：Number of quarks >＝ 4 • Hybrids：qqg，qqqg … • Glueballs：gg， ggg … Meson（ qq ） Baryon（q q q）

  5. Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established.However, during the past one year, a lot of surprising experimental evidences showed the existence of hadrons that cannot (easily) be explained in the conventional quark model.

  6. Observation of an anomalous enhancement near the threshold of mass spectrum at BES II J/ygpp BES II acceptance weighted BW +3 +5 -10 -25 M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) c2/dof=56/56 0 0.1 0.2 0.3 M(pp)-2mp (GeV) 3-body phase space acceptance Phys. Rev. Lett., 91 (2003) 022001

  7. Threshold Enhancements in J/ and B decays • They may come from different mechanism: There is “fragmentation” mechanism in B decays but NOT in J/ decays. Belle “Threshold” enhancement in B decays is much wider and is not really at threshold. It can be explained by fragmentation mechanism. BES II Threshold enhancement in J/ decays is obviously much more narrow and just at threshold, and it cannot be explained by fragmentation mechanism.

  8. NO strong dynamical threshold enhancement in cross sections (at LEAR) • With threshold kinematic contributions removed, there are very smooth threshold enhancements in elastic “matrix element” and very small enhancement in annihilation “matrix element”:  much weaker than what BES observed ! |M|2 |M|2 BES BES Both arbitrary normalization Both arbitrary normalization

  9. Any inconsistency? NO! • For example: with Mres = 1859 MeV, Γ = 30 MeV, J=0, BR(ppbar) ~ 10%, an estimation based on: At Ecm = 2mp + 6 MeV ( i.e., pLab = 150 MeV ), in elastic process, the resonant cross section is ~ 0.6 mb : much smaller than the continuum cross section ~ 94  20 mb .  Difficult to observe it in cross sections.

  10. Why can it be seen in J/ decays, but not in cross sections? • Reason is simple: J/ decays do not suffer large t-channel “background”.  It is an s-channel effect ! >>

  11. Final State Interaction ? —— Not favored • Theoretical calculation (PRD69 034004 (2003))shows: the enhancement caused by one-pion-exchange (OPE) FSI is too small to explain the BES structure. 2. The enhancement caused by Coulomb interaction is even smaller than one-pion-exchange FSI ! |M|2 |M|2 BES BES Both arbitrary normalization Both arbitrary normalization one-pion-exchange FSI Coulomb interaction

  12. pp bound state (baryonium)? There is lots & lots of literature about this possibility deuteron: baryonium: Observations of this structure in other decay modes are desirable! attractive nuclear force attractive force? + n + - loosely bound 3-q 3-q color singlets with Md = 2mp- e loosely bound 3-q 3-q color singlets with Mb = 2mp-d ?

  13. Observation of an anomalous enhancement near the threshold of mass spectrum at BES II  Data/MC The clear Λ signal in data shows high purity of signal.

  14. Phase Space Data Data

  15. S-wave BW fit results P-wave BW fit results • M = (2075 12  5) MeV Γ = (90  35  9) MeV BR = (5.9  1.4  2.0) 10-5 • M = (2044 17) MeV • Γ = (20  45) MeV • 2/d.o.f = 32.5/26 • 2/d.o.f = 31.1/26 • About 7 statistical significance high L hypotheses fail The systematic errors are carefully studied in S-wave case. accepted by P. R. L. hep-ex/0405050

  16. Near threshold enhancement is also observed in Fix the parameters, 4 away from phase space.

  17. Observation of a strong enhancement near the threshold of mass spectrum at BES II NX BES II PS, eff. corrected (Arbitrary normalization)

  18. PWA is performed to • possible N* and *states listed in PDG are fitted • N(1720), N(1900), (1520), (1690), … • manydifferent combinations are tried • different form factors are used • different JP of Nx is tried

  19. Events/10MeV Crosses: data Hist.: PWA fit projection Dalitz plot (MC) Dalitz plot (data)

  20. fit results

  21. An abnormal enhancement is observed in the mass threshold of MK • Its mass and width: (large uncertainty near threshold, high statistics is crucial!) Mass 1500~1650MeV Width70~110MeV JP favors 1/2- • large BR(J/pNx)Br(NxK) (2*10-4). What is it?? Possibly N*(1535) with large coupling to K Kmolecular state ??

  22. Light Scalar Mesons:σ, κ, f0(980), f0(1370), f0(1500), f0(1710), f0(1790)

  23. Why are light scalar mesons interesting? • There have been hot debates on the existence of  and. • Lattice QCD predicts the 0++ scalar glueball mass from 1.5 - 1.7 GeV. f0(1500) and f0(1710) are good candidates.

  24. The  pole in 0  M(+-0) M()   M(+-)

  25. Fit to J/→+ (whole mass region) Method I: Channels fitted to the data: J/f2(1270)  f0(980) b1(1235) ’(1450) f2(1565) f2(2240) b1(1235) preliminary f2 contribution f0 contribution

  26. Fit to J/→+ (M < 1.5 GeV) f2 contribution Method II: Channels fitted to the data: J/f2(1270)  f0(980) b1(1235) phase space f0 contribution

  27. Fit results: Averaged pole position: MeV accepted by P. L. B, hep-0406038

  28. at BES BES II Preliminary • BES II observed in J/K*KKK. • Preliminary PWA results Pole position:

  29. Study of f0(980), f0(1370), f0(1500), f0(1710) and f0(1790) from:

  30. f0(980) at BES • Important parameters from PWA fit: • Large coupling with KK indicates big component in f0(980) f0(980) BES II Preliminary f0(980)

  31. f0(1370) at BES • There has been some debate whether f0(1370) exists or not. • f0(1370)clearly seen in J/  , but not seen in J/  . f0(1370) BES II Preliminary NO f0(1370) PWA 0++ components

  32. f0(1710) at BES • Clear f0(1710) peak in J/  KK. • Nof0(1710) observed in J/   ! f0(1710) BES II Preliminary NO f0(1710)

  33. New f0(1790) at BES ?? • A clear peak around 1790 MeV is observed in J/  . • No evident peak in J/  KK. If f0(1790) were the same as f0(1710), we would have: Inconsistent with what we observed in J/   , KK f0(1790) BES II Preliminary ?  f0(1790) is a new scalar ??

  34. Scalars in J/  , KK Two scalars in J/  : • One is around 1470 MeV, may be f0(1500)? • The other is around 1765 MeV, is it f0(1790) or f0(1710) or a mixture of f0(1710) and f0(1790)? BES II Preliminary

  35. PWA analysis shows one scalar. Phys. Rev. D 68 (2003) 052003

  36. f0(1500) at BES • One scalar with a mass = 1466  6  16 MeV is needed in J/ , is it f0(1500)? Why the mass is different from PDG? • No peak directly seen in , KK, , KK.

  37. OZI rule and flavor tagging in J/ hadronic decays • In J/ hadronic decays, an  or  signal determinesthe or component, respectively. OZI rule

  38. Unusual properties of f0(1370), f0(1710) and f0(1790) • f0(1710): • It dominantly decays to KK (not to )  • It is mainly produced together with  (not )  • What is it ? • f0(1370) and f0(1790) • They dominantly decays to  (not to KK)  • It is mainly produced together with  (not )  • What are they ? Scalar Puzzle

  39. Excited baryon states • Probe the internal structure of light quark baryons • Search for missing baryons predicted by quark model

  40. J/ decays • relatively large branching ratios

  41. Pure isospin 1/2 Feynman diagram of the production of For and , and systems are limited to be pure isospin 1/2.

  42. The evidence of 2 new N* peaks N*(1520) N*(1535) N*(1650) N*(1675) N*(1680) N*(1440)? ? Missing mass spectrum (GeV/c2)

  43. Fitting formula : momentum of : proton momentum in Mx frame ► Possible new N* resonance ►Detailed information needs PWA Submitted to P. R. L., hep-ex/0405030

  44. Measurements of J/ and c decays

  45. c mass, width and branching ratios Phys. Lett. B 555（2003）174 – 180 Phys. Lett. B 578（2004）16 – 22

  46. Measurement of J/ → +-0 from direct J/ decay: from (2S) decay: ******************* Br(J/ →+-0) = (21.350.041.85)10-3 Br(J/ →+-0) = (20.90.21.1)10-3 Combined BES value: (21.01.1)10-3 PDG: (15.0  2.0)  10-3 inconsistent ! Phys. Rev. D 70, 012005 (2004)

  47. The branching ratio of MC Bkg K*0KS+c.c. Ks sideband signal Br(J/  KsKl ) = (1.820.040.13)10-4 PDG value： (1.080.14)10-4 Phys. Rev. D69, 012003 (2004)

  48. First observation of J/  f2(1270)f2(1270)4 fit with: BW: 0(770), f2(1270) BG: 2nd order polynomial + f2 signal J/anything MC BG M(GeV/c2) submitted to P. R. D. hep-ex/0408026

  49. Other topics

  50. Search for Lepton flavor violation (LVF) • In SM, lepton flavor symmetries are conserved. • neutrinos having mass and flavor oscillation • indicates the existence of LVF • J/  e,  and e are LVF processes Phys. Lett. B 555（2003）174 – 180 accepted by P. L. B., hep-ex/0406018

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