1. Scalar and pseudoscalar mesons at BESII Xiaoyan SHEN (Representing BES Collaboration) Institute of High Energy Physics, CAS, China Charm06, June 5-7, 2006, IHEP, Beijing

2. Scalars: , , f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710), f 0 (1790) … PWA of J/    The  threshold enhancement in J/    Study of J/    Focus on following results:

3. light scalars:  ， , f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710), f 0 (1790)

4. Why light scalar mesons are interesting? There have been hot debates on the existence of  and . Lattice QCD predicts the lightest 0 ++ scalar glueball mass ~ 1.6 GeV. f 0 (1500) and f 0 (1710) are good candidates.

5.  study  in study  in  study f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710) and f 0 (1790) in 0 ++

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

7. κ Phys. Lett. B 633 (2006) 681

8. Important parameters from PWA fit: Large coupling with KK f 0 (980) Phys. Lett. B 607 (2005) 243

9. There has been debate whether f 0 (1370) exists or not. f 0 (1370) clearly seen in J/   , but not seen in J/   . PWA 0 ++ components f 0 (1370) NO f 0 (1370) f 0 (1370) Phys. Lett. B 607 (2005) 243

10. Clear f 0 (1710) peak in J/    KK. No f 0 (1710) observed in J/    ! f 0 (1710) NO f 0 (1710) Phys. Lett. B 603 (2004) 138

11. PWA analysis shows one scalar in 1.7 GeV region Phys. Rev. D 68 (2003) 052003 f 0 (1710)

12. A clear peak around 1790 MeV is observed in J/   . No evident peak in J/    KK. If f 0 (1790) were the same as f 0 (1710), we would have: Inconsistent with what we observed in J/   ,  KK New f 0 (1790)?? f 0 (1790) ?  f 0 (1790) is a new scalar ??

13. BES II Preliminary PWA of J/    +  - and  0  0 M(  +  - ) M(  0  0 ) focus on M(  )<2.0GeV. J/    +  - and  0  0 are analyzed independently. global and bin-by-bin fits are performed. hep-ex/0603048

14. For global fit, the channels fitted in PWA  fix the parameters of f 2 (1810),f 0 (2020), f 2 (2150) and f 4 (2050) to PDG values.

15. PWA results Lower 0 ++ : 0 ++ is strongly preferred over 2 ++ f 0 (1370) cannot be excluded. f 0 (1710) or f 0 (1790) or both If interpreting the 0++ in 1.75 GeV mass region as coming from f 0 (1710)

16. all 0 ++ all 2 ++ PWA components: BES II Preliminary

17. vary the masses and widths within the errors add small components background level replace f2(1810) with f2(1950) J/  total number, tracking efficiency, kinematic fit, photon detection …… For systematic errors:

18. BES II Preliminary hep-ex/0603048

19. Observation of  threshold enhancement in J/    OZI DOZI

20. M(  +  -  0 ) M(K + K - )   M(K + K - )    M(  +  -  0 ) Dalitz plot Clear  and  signals M 2 (  ) M2()M2()

21. A clear threshold enhancement is observed Eff. curve Phase Space Side-bands Side-bands do not have mass threshold enhancement!

22. Partial Wave Analysis of J/    X, X  The amplitudes are constructed with the covariant helicity coupling amplitude method. X is parameterized by a constant width BW. BG is approximated by non-interfering phase space. The  decay information is not considered. Best fit gives: J PC (X) = 0 ++, with S-wave  X and  systems. Tried many alternative fits. The 2 ++ gives not bad likelihood value, but with more free parameters 0 ++ is favored over 0 -+ and 2 ++

23. For systematic errors: uncertainty of the BG (different treatment,..) fitting procedure (MC input and output) MC eff., total number…

24. The DOZI decay of J/  is observed and measured with 58M J/  data. An enhancement in  is found near the threshold. PWA shows: the enhancement favors 0 ++. Is it the same 0 ++ observed in  KK or , or is it a glueball, or a hybrid …..? Further look in , K*K*,  …. is desirable ! Phys. Rev. Lett., 96 (2006) 162002

26. M(  +  -  0 )(GeV/c 2 )    sideband BES II Preliminary  signal after best candidate selection (best  masses)  signal with multiple entries

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

28. Analysis of the angular distribution for the system of 2 vector mesons: signal region  sideband J P = even - is dominant in  system!

29.  (1760) f 0 (1710) f 0 (1790) f 0 (1810) PWA analysis M(  ) Total f2(1910) f2(160) BG Using observed mass and width for f 0 (1810) in J/    f 0 (1710) f 2 (1910) 5.8  f 2 (1640) 5.5  BG  (1760) > 10  f 0 6.5  M(  ) (GeV/c 2 )

30.  dominated by  (1760)  a 0 ++ is possible needed (6.5  ) Accepted by PRD, hep-ex/0604045

31. Summary   and , f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710), … are studied  PWA of J/     the observation of  threshold enhancement f 0 (1810) in J/      (1760) dominant in J/   , possible existence of f 0 at around 1800 GeV.

32. Thanks!