Recent Charmonium Physics from BES

Abstract

Measurements of branching fractions for nine different final states, based on a data sample of approximately 4 million psi(2S) events collected with the BESI detector at the BEPC, are reported. Using the same event sample, radiative decays of the psi (2S) into pi pi, K K-bar and eta eta final states have been measured. Cross sections for e e -> e e, hadrons, pi pi J/psi, and mu mu have been measured in the vicinity of the psi(2S) resonance using the BESII detector. The psi(2S) total width; partial widths to hadrons, pi pi J/psi and muons; and corresponding branching fractions have been determined. Decays of J/psi -> gamma eta_c are used to determine the mass and width of the eta_c using a sample of 58 M J/psi events. $M_{η_c} = (2977.5 \pm 1.0 \pm 1.2)$ MeV and $Γ_{η_c} = (17.0 \pm 3.7 \pm 7.4)$ MeV. The first observation of chicJ (J=0,1,2) decays to lambda lambda-bar is reported using psi(2S) data collected with the BESII detector. Results are compared with model predictions.