Based on (3.79 4-0.31) × 106 ¢/data sets collected with the BES detector at BEPC, the recent ¢i, XcJ and y~ results from BES are presented.
1. STUDIES OF ¢' DECAYS
Charmonium physics is always one of the interesting and intriguing fields of particle physics. Charmonium provides us an excellent and simple system to study QCD, the production and decay mechanisms of heavy quarkonia and light hadron spectra from its decays, and can be treated nonreIativistically and perturbatively. Using (3.79 4-0.31) × 106 ¢' sample collected with the BEijing Spectrometer (BES) at BEPC, the recent ¢', Xc and y~ results are presented. The BES detector is described in detail in Ref. [1].
Out of the charmonium decays, there exists a mysterious and longstanding plr puzzle of J/¢ and ¢' decays [2]~ first revealed by Mark-II Collaboration. In QCD, both ¢' and J/¢ decays are expected to be dominated by annihilations into three gluons. Based on the similarity between the ¢' and J/¢ wave functions and the slow running of the strong interaction coupling constant as, the non-relativistic perturbative QCD predicts [3]: the ratios of the decays widths of ¢/into hadrons to those of J/¢ into hadrons are: * p~r * K+K*(892) -+ c.c. * K°~*(892) ° + c.c. * 097f0 * ~or] * ,Kd-.K--7~0 * KKTr * (9,7£+,]r-* ¢f0(980) * ¢aTr+ ./r -* wK+K -* (Mpp * Cpp * ,ff-bTf--TcOp~ * rpr+Tc-pp * ypp * Br(xe2 --+ 7r °TrO) *B~(xoo ~ ,7,7) * Br(x~ ~ '7'7)
The mass differences between Xco,1,2 and between 7/c and J/~b reflect the hyperfine structure of the spin-spin interactions, the X~1,2 and J/¢ masses have been precisely determined. BES improves [13] the X~o mass with (3414.1 4-0.6 4-0.8) MeV over PDG98 value with an error of 2.8 MeV, and Xco decay width with P×~0 = (14.3 5: 3.6) MeV over PDG98 value (13.5 4-5.3 MeV). Fig. 2 shows Xc3 hadronic decays [13,14]. From ¢' radiative transition to r/c, BES gives the qc mass with (2975.8 + 3.9 4-1.2) MeV [14].