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New Observations and Multiquark Candidates at BESII

New Observations and Multiquark Candidates at BESII. HongXun Yang (for BES Collaboration) Institute of High Energy Physics (IHEP) yanghx@mail.ihep.ac.cn CPS2006 BEIJING, Sept. 16, 2006. J/  decays are an ideal factory to search for and study light exotic hadrons:.

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New Observations and Multiquark Candidates at BESII

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  1. New Observations and Multiquark Candidates at BESII HongXun Yang (for BES Collaboration) Institute of High Energy Physics (IHEP) yanghx@mail.ihep.ac.cn CPS2006 BEIJING, Sept. 16, 2006

  2. J/ decays are an ideal factory to search for and study light exotic hadrons: • The production cross section of J/ is high. • The production BR of hadrons in J/ decays are one order higher than ’ decays (“12% rule”). • The phase space to 1-3 GeV hadrons in J/ decays are larger than  decays. • Exotic hadrons are naively expected to have larger or similar production BR to conventional hadrons in J/ decays. • Clean background environment compared with hadron collision experiments, e.g., “JP, I” filter.

  3. World J/ Sample (106) Largest from BES 2001

  4. Outline • A possible bound state: mass threshold enhancement in and new observation of X(1835). • mass threshold enhancement in • mass threshold enhancementin •  mass threshold enhancement in J/   • New observation of a broad 1- - resonance in J/  K+K- 0

  5. A possible ppbar bound state

  6. 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

  7. This narrow 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.: No enhancement near threshold

  8. This narrow 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. No narrow strong enhancement near threshold

  9. Pure FSI disfavored I=0 S-wave FSI CANNOT fit the BES data. FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005) in the fit (I=0) FSI* PS * eff + bck

  10. X(1860) has large BR to ppbar • We (BES) measured: • From Crystal Ball result, we etimate: • So we would have: (This would be the largest BR to ppbar among all known mesons) Considering that decaying into ppbar is only from the tail of X(1860) and the phase space is very small, such a BR indicates X(1860) has large coupling to ppbar !

  11. Summary of the properties of the strong ppbar mass threshold enhancement X(1860) • So far, it is only observed in J/ radiative decays: • It has production properties similar to ’ meson. • It could have strong coupling to gluons as ’ meson. • It could have the largest decay BR to ppbar among all PDG particles: • It has strong coupling to ppbar.

  12. New Observation of X(1835) in PRL 95, 262001 (2005)

  13. Observation of X(1835) in Statistical Significance 7.7  The +- mass spectrum for  decaying into +- and  

  14. Mass spectrum fitting The +- mass spectrum for  decaying into +- and   7.7 BESII Preliminary

  15. 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)

  16. A Possible ppbar Bound State • X(1835) could be the same structure as ppbar mass threshold enhancement. • 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.

  17. Observation of mass threshold enhancement in

  18. Phys. Rev. Lett. 93, 112002 (2004) Observation of an anomalous enhancement near the threshold of mass spectrum at BES II BES II 3-body phase space For a S-wave BW fit: M = 2075 12  5 MeV Γ = 90  35  9 MeV

  19. K mass threshold enhancement

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

  21. 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.

  22. 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)

  23. The KΛ mass threshold enhancement NX(1610) could be a KΛ bound/resonant state (5-quark system with hidden ssbar components).

  24. Observation of mass threshold enhancement

  25. We studied DOZI process: J/    +  +    +-0 K+ K-

  26. Clear  and  signals    recoiling against 

  27. Dalitz Plot

  28. Phys. Rev. Lett. 96, 162002 (2006) A clear mass threshold enhancement is observed Acceptance

  29. 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)?

  30. Is the STRONG threshold enhancement universal/naïve in J/ decays ?——NO ! • Actually in many other cases we do NOT see STRONG threshold enhancements ! • For example: In J/ decays at BES II

  31. hep-ex/0606047, Submitted to Phys. Rev. Lett. New observation of a broad 1- - resonance in J/  K+K- 0

  32. J/  K+K- 0 very clean 0 signal

  33. J/  K+K- 0 Background PID and kinematic fit can significantly reduce the dominant background from J/  + - 0.

  34. 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 ( preliminary ): ( can be ruled out by much worse likelihood ) • X pole position • big destructive interference among and PS

  35. 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).

  36. 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.

  37. Summary (I) • BES II has observed several strong mass threshold enhancements in J/ decays. • Why strong mass threshold structures are important? Multiquark states may be only observable near mass thresholds with limited decay phase space.  Otherwise, it might be too wide to be observed as a resonance since it can easily fall apart into two or more mesons. I can see f0(980) I can see broad  under other peaks any broad resonance under other peaks? broad resonance or phase space?

  38. Summary (II) • A very narrow and strong mass threshold enhancement is uniquely observed in decays at BES II: • It is NOT observed in Y(1S) decays, nor in J/psi hadronic decays. FSI is strongly disfavored. • Its large BR to suggests it be a bound state. • X(1835) is observed in It could be same structure as the ppbar mass threshold enhancement, i.e., it could be a ppbar bound state.

  39. Summary (III) • mass threshold enhancement was observed in • Evidence of NX(1610) was observed near KΛmass threshold, suggesting a KΛ bound or resonant state. • An  mass threshold enhancement was observed in J/  . • A very broad 1- - resonance X(1580) is observed in J/  K+K- 0 . J/ψ decay is an ideal place to study exotic structures.

  40. 谢 谢！Thank You!

  41. Multi-quark State, Glueball and Hybrid • 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） How quarks/gluons form a hadron is far from being well understood.

  42. Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established.However, during the past two years, a lot of surprising experimental evidences showed the existence of hadrons that cannot (easily) be explained in the conventional quark model. Most of them are multi-quark candidates. Searching for multi-quark states becomes one of the hottest topics in the hadron spectroscopy.

  43. What do we expect from J/psigamma ppbar results? The baryonium interpretation of the ppbar mass threshold enhancement predicts a new particle around 1.85 GeV which should be observed in other decay mode with full BW resonant structure.

  44. Possible Interpretations • FSI？ Theoretical calculations are needed. • Conventional K* or a multiquark resonance？ • Search for its Kπ 、Kππ decay modes would help to understand its nature. • We are now studying J/ KKπ 、KKππ

  45. 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

  46. 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 experimentally.

  47. This narrow threshold enhancement is NOT observed in B decays • The structure in B decays is obviously different from the BES observation: Belle The structure 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.

  48. Pure FSI disfavored (I) • Theoretical calculation (Zou and Chiang, PRD69 034004 (2003))shows: The enhancement caused by one-pion-exchange (OPE) FSI is too small to explain the BES structure. • 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

  49. FSI Factors Most reliable full FSI factors are from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005)，which fit ppbar elastic cross section near threshold quite well. ppbar elastic cross section near threshold I=1 S-wave P-wave I=0 S-wave

  50. In ppbar collision, the background is much lager (I) • J/ decays do not suffer large t-channel “background” as ppbar collision. >>

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