1. Resent BES Results on Scalar Mesons Zhipeng Zheng (Representing BES Collaboration) Institute of High Energy Physics, CAS GHP-2004, Oct. 25

2. OUTLINE Introduction  and  f 0 (980) f 0 (1370), f 0 (1500), f 0 (1710) and f 0 (1790) Summary

3. Introduction (1) Why are light scalar mesons interesting? The knowledge on the light scalars is very important to the understanding of QCD in nonperturbative region There have been hot debates on the existence of  and .

4. f 0 (980) : precise parameters m,  …. are needed. Is it a state, or molecular or four quark state? Lattice QCD predicts the 0 ++ scalar glueball mass from 1.5 - 1.7 GeV. f 0 (1500) and f 0 (1710) are good candidates. Introduction (2)

5. f 0 (1370), f 0 (1500), f 0 (1710) were found in the fixed target,, e + e - experiments. The confirmation of them is important. f 0 (1500), f 0 (1710) are treated as mixed state of glueball with meson, but we need more information. The BESII data have much higher statistics and lead to a much more decisive partial wave analysis. Introduction (3)

6. BESII Detector 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+p 2 )  z = 2.3 cm  counter:  r  = 3 cm B field: 0.4 T  z = 5.5 cm J/   (2S) World J/  and  (2S) Samples (×10 6 ) BESII 58M J/  BESII 14M  (2S) Introduction (4)

7. M(  ) M(  +  -  0 ) M(  +  - ) 00    The  pole in J/  +  - f 2 (1270)

8. Fit Method I: (whole mass region) f 0 contribution b 1 (1235) Channels fitted to the data: J/  f 2 (1270)   f 0 (980) b 1 (1235)   ’(1450)  f 2 (1565)  f 2 (2240)  f 2 contribution

9. Fit to J/  →  +   (M  < 1.5 GeV) Channels fitted to the data: J/  f 2 (1270)   f 0 (980) b 1 (1235)  P.S f 0 contribution f 2 contribution Fit Method II: (M  <1.5GeV)

10. Breit-Wigner for  in the fit: (1) (2) (3) (4)

11. Averaged pole position: P. L. B 598 (2004) 149-158 Method I Method II Fit Result

12.  in J/  K +  - K +  - K 0 *(1430), K 2 *(1430)K*(892) ρ(770) K 1 (1270), K 1 (1400)

13.  in J/  K +  - K +  - K* 0 (1430)  K*K*

14.  in 

15. f 0 (980) in J/  +  -,  K + K - Important parameters from PWA fit: Large coupling with KK indicates big component in f 0 (980) f 0 (980) f 0 (1370) f 2 (1525) BESII preliminary

16. There has been some debate whether f 0 (1370) exists or not. f 0 (1370) clearly seen in J/   , but not seen in J/   . f 0 (1370) NO f 0 (1370) f 0 (1370) in J/  +  -,  +  - PWA 0 ++ components f 0 (980) f 2 (1270) BESII preliminary

17. f 0 (1500) in J/  +  -,  0  0 One scalar with a mass = 1466  6  16 MeV is needed in J /   . It’s also needed in the fit of J /   ,  kk No peak directly seen in ,  KK, ,  KK channels. f 2 (1270) f 0 (1500) f 0 (1710) BESII preliminary

18. f 0 (1710) in PWA analysis shows one scalar. Phys. Rev. D 68 (2003) 052003 f 0 (1710) f 2 (1525)

19. f 0 (1710) in J/  The scalar around 1710MeV with mass Combine the branching ration of  and  kk, we obtain: f 2 (1270) f 0 (1710) f 2 (1270) f 0 (1710) BESII preliminary

20. f 0 (1710) in J/  K + K -,  +  - Clear f 0 (1710) peak in J/    KK. No f 0 (1710) observed in J/    ! f 0 (1710) NO f 0 (1710) f 2 (1270) PWA 0 ++ components hep-ex/0409007

21. 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! f 0 (1790) ? f 0 (1790) in J/  K + K -,  +  - f 0 (1710) BESII preliminary

22. Summary of Scalar Meson at BES Summary  Clear seen(peak + fit)  in the fit

23. The existence of  is confirmed in J/  +  - with pole position: Evidence for the  as a peak close to threshold. Pole position: Summary

24. f 0 (980) is clearly seen in both  +  -,  K + K - data, parameters of f 0 (980) are well determined. Summary

25. f 0 (1370) is clearly seen in J/  +  -, But not evidence in J/  +  - f 0 (1500) is seen in J/  channel with mass: f 0 (1710) is clearly seen in J/   KK with mass and width: Summary

26. f 0 (1710) is also seen in the J/ , and  K + K, but not seen in J/   +  - f 0 (1790) is needed in the fit of J/   +  -, and need more study. Summary