Resent BES Results on Scalar Mesons Zhipeng Zheng (Representing BES Collaboration) Institute of High Energy Physics, CAS GHP-2004, Oct. 25
OUTLINE Introduction and f 0 (980) f 0 (1370), f 0 (1500), f 0 (1710) and f 0 (1790) Summary
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 .
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 GeV. f 0 (1500) and f 0 (1710) are good candidates. Introduction (2)
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)
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)
M( ) M( + - 0 ) M( + - ) 00 The pole in J/ + - f 2 (1270)
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
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)
Breit-Wigner for in the fit: (1) (2) (3) (4)
Averaged pole position: P. L. B 598 (2004) Method I Method II Fit Result
in J/ K + - K + - K 0 *(1430), K 2 *(1430)K*(892) ρ(770) K 1 (1270), K 1 (1400)
in J/ K + - K + - K* 0 (1430) K*K*
in
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
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
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
f 0 (1710) in PWA analysis shows one scalar. Phys. Rev. D 68 (2003) f 0 (1710) f 2 (1525)
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
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/
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
Summary of Scalar Meson at BES Summary Clear seen(peak + fit) in the fit
The existence of is confirmed in J/ + - with pole position: Evidence for the as a peak close to threshold. Pole position: Summary
f 0 (980) is clearly seen in both + -, K + K - data, parameters of f 0 (980) are well determined. Summary
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
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