Study of Scalar Mesons at BES Xiaoyan SHEN
Study of Scalar Mesons at BES Xiaoyan SHEN Representing BES Collaboration Institute of High Energy Physics, CAS QWG 3 Oct. 12 – 15, 2004, Beijing
Outline n Introduction n Light Scalar Mesons: , f 0(980) f 0(1370) f 0(1500) f 0(1710), f 0(1790) n Summary
Introduction BESII Detector World J/ and (2 S) Samples (× 106) BESII 58 M J/ VC: xy = 100 m TOF: T = 180 ps MDC: xy = 220 m BSC: E/ E= 21 % d. E/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 BESII 14 M (2 S)
Light Scalar Mesons: σ, κ, f 0(980), f 0(1370), f 0(1500), f 0(1710), f 0(1790)
Why are light scalar mesons interesting? n There have been hot debates on the existence of and . n Lattice QCD predicts the 0++ scalar glueball mass from 1. 5 - 1. 7 Ge. V. f 0(1500) and f 0(1710) are good candidates. n f 0(1370), f 0(1500), f 0(1710) were found in the fixed target, ppbar, e+e- experiments. The confirmation of them is important.
The pole in 0 M( ) M( + -) M( + - 0)
Breit-Wigner for :
Fit to J/ → + (whole mass region) Method I: 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) preliminary f 2 contribution f 0 contribution
Fit to J/ → + (M < 1. 5 Ge. V) f 2 contribution Method II: Channels fitted to the data: J/ f 2(1270) f 0(980) b 1(1235) phase space f 0 contribution
Fit results: Method II Averaged pole position: Me. V P. L. B 598 (2004) 149 -158
ρ(770) K*(892) K 0*(1430), K 2*(1430) K 1(1270), K 1(1400)
ary BES Prelimin K*0(1430) κ
ary BES Prelimin κ
Study of f 0(980), f 0(1370), f 0(1500), f 0(1710) and f 0(1790) from:
f 0(980) at BES n f 0(980) S E B r P II Important parameters from PWA fit: ry a in m eli f 0(980) n Large coupling with KK indicates big component in f 0(980)
f 0(1370) at BES n There has been some debate whether f 0(1370) exists or not. n f 0(1370) clearly seen in J/ , but not seen in J/ . f 0(1370) S E B PWA 0++ components r P II ry a in m eli NO f 0(1370)
f 0(1710) at BES n Clear f 0(1710) peak in J/ KK. n No f 0(1710) observed in J/ ! f 0(1710) ry a in BE I I S im l e Pr NO f 0(1710)
New f 0(1790) at BES ? ? n A clear peak around 1790 Me. V is observed in J/ . n No evident peak in J/ KK. If f 0(1790) were the same as f 0(1710), we would have: f 0(1790) ry a in I S BE I im l e Pr ? Inconsistent with what we observed in J/ , KK Is f 0(1790) a new scalar ? ?
Scalars in J/ , KK Two scalars in J/ : ¨ One is around 1470 Me. V, => f 0(1500) r ry a in m eli S E B II P ¨ The other is around 1765 Me. V, is it f 0(1790) or f 0(1710) or a mixture of f 0(1710) and f 0(1790)?
PWA analysis shows one scalar. Phys. Rev. D 68 (2003) 052003
ary BES Prelimin
f 0(1500) at BES n One scalar with a mass = 1466 6 16 Me. V is needed in J/ . f 0(1500). n No peak directly seen in , KK, , KK.
OZI rule and flavor tagging in J/ hadronic decays n In J/ hadronic decays, an or signal determines the or component, respectively. OZI rule
Unusual properties of f 0(1370), f 0(1710) and f 0(1790) n f 0(1710): ¨ It dominantly decays to KK (not to ) ¨ It is mainly produced together with (not ) ¨ What is it ? n f 0(1370) ¨ They ¨ It and f 0(1790) dominantly decays to (not to KK) is mainly produced together with (not ) ¨ What are they ? Scalar Puzzle – no good answer yet!
Summay pole obtained in J/ n pole in J/ K*K and KK n the parameters of f 0(980) are determined n scalar puzzle? Further study needed. n
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