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New Results and Prospects of Light Hadron Spectroscopy

This presentation discusses new results on mesons and baryons in light hadron spectroscopy, as well as prospects for glueball searches. Topics include new measurements of 0-+, 0++, and 1-- mesons, as well as the observation of X(1835) and a mass threshold enhancement in the ωφ decay. The production properties of X(1860) and f0(1500) are also explored.

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New Results and Prospects of Light Hadron Spectroscopy

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  1. New Results and Prospectsof Light Hadron Spectroscopy Shan JIN Institute of High Energy Physics (IHEP) jins@mail.ihep.ac.cn Presented by Yi-Fang Wang Charm 2007 Ithaca, August 7, 2007

  2. Outline • New results on 0-+ mesons • New results on 0++ mesons • New results on 1-- mesons • New results on baryons at BESII • Prospects of glueball searches at BESIII

  3. New results on 0-+ mesons

  4. (1760) in at BESII

  5. Phys. Rev. D 73 (2006) 112007   M(+-0)(GeV/c2) M(+-0)(GeV/c2) M(+-0)(GeV/c2) M(+-0)(GeV/c2)  sideband  signal with multiple entries  signal after best candidate selection (best w masses)

  6. M() M() Side-band Phase Space Eff. curve

  7. PWA analysis f0(1710) f0(1790) f0(1810) Total (1760) > 10  f0 (1760) f0(1710) Using observed mass and width for f0(1810) in J/  f2(1640) f2(1910) f2(160) f2(1910) BG BG M() M() (GeV/c2)

  8. The existence of (1760) is confirmed • Its mass and width were first correctly measured with PWA. Phys. Rev. D 73 (2006) 112007

  9. Candidate of 0-+ baryonium

  10. Phys. Rev. Lett. 95, 262001 (2005) Observation of X(1835) in at BESII Statistical Significance 7.7  The +- mass spectrum for  decaying into +- and  

  11. Phys. Rev. Lett. 91, 022001 (2003) 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

  12. Re-fit to J/p pbar including FSI Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005) in the fit (I=0) M = 1830.6  6.7 MeV  < 153 MeV @90%C.L. In good agreement with X(1835)

  13. Candidate of 0-+ ppbar Bound State • X(1835) could be the same structure as ppbar mass threshold enhancement X(1860)/X(1830). • It could be a ppbar bound state since it dominantly decays to ppbar when its mass is above ppbar mass threshold. • Its spin-parity should be 0-+: this would be an important test. There is already an (1760) nearby , so that  X(1835) is very likely to be an unconventional 0-+ meson.

  14. This strong threshold enhancement is NOT observed in at CLEO • This result cannot be explained by pure FSI effect, since FSI is a universal effect. FSI interpretation of the narrow and strong ppbar threshold enhancement is disfavored. • This indicates that X(1860) has a production property similar to ’ meson. c.f.: Phys.Rev.D73, 032001(2006) No enhancement near threshold

  15. No strong threshold enhancement is observed in at BESII • FSI interpretation of the narrow and strong ppbar threshold enhancement is disfavored. • This again indicates that X(1860) has a production property similar to ’ meson. c.f.: Phys.Rev.Lett.99, 011802 (2007) No significant narrow strong enhancement near threshold (2.0  if fitted with X(1860))

  16. This strong threshold enhancement is NOT observed in at BESII • This again disfavors FSI and indicates that X(1860) has a production property similar to ’ meson. c.f.: • This also indicates X(1860) may have strong coupling to gluons as ’ meson. BESII Preliminary No narrow strong enhancement near threshold

  17. Summary of new studies on ppbar mass threshold structure X(1860) • Pure FSI effect cannot explain X(1860) structure. • X(1860) has production properties similar to ’ meson  • Why a baryonium (candidate) has a production properties similar to ’ meson? • ’ excitation? Why an ’ excitation dominantly decays into ppbar above ppbar mass threshold?

  18. New results on 0++ mesons

  19. Observation of  mass threshold enhancement at BESII Phys. Rev. Lett. 96,162002 (2006)

  20.   recoiling against  J/    +  +    +-0 K+ K- • We studied DOZI process:

  21. Side-bands A clear mass threshold enhancement is observed Acceptance

  22. The radiative decay of J/ has been observed in the 58M J/ data. • A significant structure of  has been found near the mass threshold. • PWA shows the structure favors 0++, with a mass , width 1052028 MeV, and the corresponding branch ration is (2.610.270.65)x10-4. • It could be a multiquark/hybrid/glueball state. • Its relation with f0(1710),f0(1790)?

  23. PWA of J/  +- and 00 at BESII Phys. Lett. B 642 (2006) 441

  24. PWA of J/  +- and 00 The channels fitted in PWA: M(+- ) M(00 )

  25. PWA components: all 2++ all 0++

  26. PWA results • Lower 0++ : 0++ is strongly preferred over 2++ • f0(1370) cannot be excluded. • Higher 0++: f0(1710) or f0(1790)

  27. Phys. Lett. B 642 (2006) 441

  28. About f0(1500) • It is first clearly observed in J/psi radiative decays. • Its production rate in J/psi radiative decays: • The production rate of f0(1500) in J/psi radiative decays is lower than f0(1710): • It indicates f0(1710) has stronger coupling to gluons than f0(1500) which one contains more glueball content?

  29. New results on 1-- mesons

  30. New observation of a broad 1-- resonance in J/  K+K- 0 at BESII Phys. Rev. Lett. 97 (2006) 142002

  31. K*(1410) 0 X(1580) K*(892) 0 sideband background ? J/ K+K-0 PID and kinematic fit can significantly reduce the dominant background from J/  + - 0.

  32. Partial Wave Analysis of J/  K+K- 0 events • Four decay modes are included : • Amplitudes are defined by Covariant tensor formalism B.S. Zhou and D.V. Bugg, Eur. Phys. J. A16, 537(2003) • BW with energy-dependent width J.H. Kuhn, A. Satamaria, Z. Phys. C48, 445 (1990).

  33. Partial Wave Analysis of J/  K+K- 0 events • Parity conservations in J/  K+K- 0requires that spin-parity of K+K- should be 1--,3--,… • PWA fit with and phase space (PS) gives: ( can be ruled out by much worse likelihood ) • X pole position • big destructive interference among and PS

  34. Broad X cannot be fit with known mesons or their interference • It is unlikely to be (1450), because: • The parameters of the X is incompatible with (1450). • (1450) has very small fraction to KK. From PDG: • It cannot be fit with the interference of (770) , (1900) and (2150): • The log-likelihood value worsens by 85 (2=170).

  35. How to understand broad X(1580)? • Search of a similar structure in J/  KSK will help to determine its isospin. • X(1580) could have different nature from conventional mesons: • There are already many 1- - mesons nearby. • Width is much broader than other mesons. • Broad width is expected for a multiquark state.

  36. A structure at 2175MeV was observed in e+e-f0(980), via initial-state radiation at BABAR. Evidence of a new 1-- resonance Y(2175) at BaBar Phys. Rev. D 74 (2006) 091103(R)

  37. What is Y(2175)? • A conventional state? • An analog of Y(4260) ( )? • An 4-quark state? • More experimental information needed, especially we can search for it in J/psi decays at BESII and BESIII.

  38. New results on baryons at BESII

  39. N* in . at BESII 0 BES II Preliminary  M2(p0) M

  40. BES II Preliminary N* in . Resonances used in the PWA The best results to now

  41. N* in . BES II Preliminary  data  Fit results Fit results agree with data reasonably, especially in the low mass region. The comparison between data and PWA fit results.

  42. N* in . BES II Preliminary

  43. K mass threshold enhancement

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

  45. A strong enhancement is observed near the mass threshold of MKat BES II. • Preliminary PWA with various combinations of possible N* and Λ* in the fits —— The structure Nx*has: Mass 1500~1650MeV Width70~110MeV JP favors 1/2- The most important is: It has large BR(J/ψ  pNX*) BR(NX* KΛ)2 X 10-4 , suggesting NX* has strong coupling to KΛ.

  46. Nx* is N(1535)? • From: If Nx* is N(1535), we would have Then N(1535) would have very large ssbar component (a 5-quark system).

  47. Such a big coupling to K of N(1535) is NOTobserved in process at SAPHIR Phase Space shape

  48. A ΛK resonance predicted by chiral SU(3) quark model • Based on a coupled-channel study of ΛK andΣK states in the chiral SU(3) quark model, the phase shift shows the existence of a ΛK resonance between ΛK andΣK mass threshold. ( F. Huang, Z.Y. Zhang et al. Phys. Rev. C71: 064001, 2005 ) Ecm – ( MΛ+MK ) (MeV)

  49. The KΛ mass threshold enhancement NX(1610) could be a KΛ bound/resonant state. • Whether NX(1610) is N(1535) needs further study.

  50. Study of at BESII • No obvious N* in Dalitz plot. • We measured: BES II Preliminary

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