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Study of Scalar Mesons at BES

Study of Scalar Mesons at BES. Xiaoyan SHEN Representing BES Collaboration Institute of High Energy Physics, CAS QWG3 Oct. 12 – 15, 2004, Beijing. Outline. Introduction Light Scalar Mesons:  ,  f 0 (980) f 0 (1370) f 0 (1500) f 0 (1710), f 0 (1790)

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Study of Scalar Mesons at BES

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  1. Study of Scalar Mesons at BES Xiaoyan SHEN Representing BES Collaboration Institute of High Energy Physics, CAS QWG3 Oct. 12 – 15, 2004, Beijing

  2. Outline • Introduction • Light Scalar Mesons:,  f0(980) f0(1370) f0(1500) f0(1710), f0(1790) • 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. Light Scalar Mesons:σ, κ, f0(980), f0(1370), f0(1500), f0(1710), f0(1790)

  5. 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. • f0(1370), f0(1500), f0(1710) were found in the fixed target, ppbar, e+e- experiments. The confirmation of them is important.

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

  7. Breit-Wigner for :

  8. 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

  9. 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

  10. Fit results: Method I Method II Averaged pole position: MeV P. L. B 598 (2004) 149-158

  11. ρ(770) K*(892) K0*(1430), K2*(1430) K1(1270), K1(1400)

  12. BES Preliminary K*0(1430) κ

  13. BES Preliminary κ

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

  15. 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)

  16. 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

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

  18. 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 ?  Is f0(1790) a new scalar ??

  19. Scalars in J/  , KK Two scalars in J/  : • One is around 1470 MeV, => 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

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

  21. BES Preliminary BES Preliminary

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

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

  24. 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 – no good answer yet!

  25. Summay •  pole obtained in J/ •  pole in J/K*K and KK • the parameters of f0(980) are determined • scalar puzzle? Further study needed.

  26. Thank you! 谢谢！

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