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Recent BESII Results Representing BESII Collaboration Weiguo Li

Recent BESII Results Representing BESII Collaboration Weiguo Li Institute of High Energy Physics, Beijing 100049, P.R. China liwg@ihep.ac.cn NSTAR Workshop Bonn, Sep. 6, 2006. Outline Introduction Light Hadron Spectroscopy from J/ Decays Study of Excited Baryon States

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Recent BESII Results Representing BESII Collaboration Weiguo Li

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  1. Recent BESII Results Representing BESII Collaboration Weiguo Li Institute of High Energy Physics, Beijing 100049, P.R. China liwg@ihep.ac.cn NSTAR Workshop Bonn, Sep. 6, 2006

  2. Outline • Introduction • Light Hadron Spectroscopy from J/ Decays • Study of Excited Baryon States • Selected BF Measurements • Summary

  3. BESII Detector VC: xy = 100 m TOF: T = 180 ps counter: r= 3 cm MDC: xy = 250 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.4 %  = 7.9 mr B field: 0.4 T p/p=1.8(1+p2) z = 2.3 cm Dead time/event: 〈10 ms

  4. Data from BESII BESII finished data taking April 2004

  5. Light Hadron Spectroscopy from J/ Decays • Scalars: ,  clearly observed • X(1835) in J/  ’ • The  threshold enhancement in J/   • New observation of a broad 1- - resonance in J/  K+K- 0 •  (1760) in J/   

  6. The  pole in at BESII 0 M(+-0)  M()  M(+-)  Averaged pole position: MeV Phys. Lett. B 598 (2004) 149

  7. κ Phys. Lett. B 633 (2006) 681

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

  9. 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

  10. Re-fit to J/pp 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)

  11. Candidate of 0-+ pp Bound State • X(1835) could be the same structure as pp mass threshold enhancement X(1860)/X(1830). • It could be a pp bound state since it dominantly decays to pp when its mass is above pp 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.

  12. 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. • This indicates that X(1860) has a production property similar to ’ meson. Phys.Rev.D73, 032001(2006) No enhancement near threshold

  13. 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. Phys.Rev.Lett.99, 011802 (2007) No significant narrow strong enhancement near threshold (2.0  if fitted with X(1860))

  14. J/ pp Clear  signal is seen, B(J/ pp) =( 9.8  0.3  1.4 )  10–4 B(J/ X(1860))B(X(1860) pp) < 1.5  10–5 @ 95% C.L. BES II Preliminary

  15. 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. • This also indicates X(1860) may have strong coupling to gluons as ’ meson.

  16. Summary of new studies on pp 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?

  17.   recoiling against   mass threshold enhancement • We studied DOZI process: J/    +  +    +-0 K+ K- Phys. Rev. Lett. 96,162002 (2006)

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

  19. 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++, M = ,  =1052028 MeV, and the corresponding branch fraction = (2.610.270.65)x10-4. • It could be a multiquark/hybrid/glueball state. • Its relation with f0(1710), f0(1790)?

  20. New observation of a broad 1– resonance in J/  K+K- 0 K*(1410) 0 X(1580) K*(892) 0 sideband background ? PID and kinematical fit can significantly reduce the dominant background from J/  + - 0. Phys. Rev. Lett. 97 (2006) 142002

  21. 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). Phys. Rev. Lett. 97 (2006) 142002

  22. 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

  23. 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).

  24. 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 multi-quark state.

  25. 0-+ Meson 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  masses)

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

  27. 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)

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

  29. Study of Excited Baryon States Motivation • Probe the internal structure of light quark baryons • Search for missing baryons predicted by quark model • Obtain a better understanding of the strong interaction force in the non-perturbative regime

  30. Experimental Advantages • relatively large branching ratios 58 M J/ and 14 M (2S) at BES II

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

  32. N* in. Phys. Rev. Lett. 97, 062001 (2006)

  33. N*(1520) N*(1535) N*(1650) N*(1675) N*(1680) N*(1440) ? N* in +c.c. L=0 limits it to be 3/2+ or 1/2+

  34. N* in +c.c. • About 10 K events are selected • N*(1440) is observed directly in the mass spectrum • Possible new N* resonance • L=0 limits it to be 3/2+ or 1/2+ • Detailed information need PWA

  35. Large accumulation below 1.5 GeV/c2，which may be due to N(1440), N(1520),N(1535) etc. • The cluster above 2 GeV/c2 is partlydue to the reflection of N(1440) etc.,and partly may due to high mass N*. • No clear N(2065) peak, but we can notrule out its existence. Phys. Rev. D74, 012004 (2006)

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

  37. N* in. BES II Preliminary

  38. N* in. Resonances used in the PWA BES II Preliminary

  39. N* in.  data  Fit results BES II Preliminary Fit results agree with data reasonably, especially in the low mass region.

  40. N* in. BES II Preliminary Optimized masses and widths, other resonances are fixed.

  41. N* in. • More than 10 K events were selected, and detailed PWA was performed • N(2065) is needed in the fit, and JPC favor 3/2+ • Only N(1710) is needed in the M = 1.7 GeV region • The masses and widths of some other N* have also been given

  42. 0  Phys. Rev. D71, 072006 (2005) • A faint accumulation of events around 2065 MeV/c2 • The enhancement between 1.4 and 1.7 GeV/c2 • Possible N*(1535) in the p invariant mass

  43. Phys. Rev. Lett. 93, 112002 (2004) For a S-wave BW fit: M = 2075 12  5 MeV Γ = 90  35  9 MeV

  44. N*(1535)? N*(1650)? *(1520) *(1690) PS, eff. corrected (Arbitrary normalization) BES II Preliminary • Two clear peaks at 1520, 1690 MeV/c2 in pK mass • N* in K mass • PWA is being performed

  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 , suggestingNX* has strong coupling to KΛ.

  46. 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 aΛK resonance between ΛK andΣK mass threshold. ( F. Huang, Z.Y. Zhang et al. Phys. Rev. C71: 064001, 2005 ) Ecm – ( MΛ+MK ) (MeV)

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

  48. BES II Preliminary KS

  49. A enhancement near S threshold is evident • N* and * found in the S and nS spectrum * N* BES II Preliminary

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