Recent Charmonium Physics from BES

Measurements of branching fractions for ψ(2S) decays into ωππ, b1π, ωf2(1270), ωKK, ωpp̄, φππ, φf0(980), φK K, and φpp̄ final states, based on a data sample of (4.02 ± 0.22) × 10 ψ(2S) events collected with the BESI detector at the Beijing ElectronPositron Collider, are reported. Using the same event sample, radiative decays of the radially excited charmonium resonance, ψ(2S), into ππ, KK and ηη final states have been measured. The branching ratios B(ψ(2S) → γf2(1270)) = (2.12± 0.19± 0.32)× 10 −4 and B(ψ(2S) → γf0(1710)) ×B(f0(1710) → K K) = (3.02± 0.45 ± 0.66) × 10 are obtained. Cross sections for ee → ee, hadrons, ππJ/ψ, and μμ have been measured in the vicinity of the ψ(2S) resonance using the BESII detector. The ψ(2S) total width; partial widths to hadrons, ππJ/ψ, and muons; and corresponding branching fractions have been determined to be Γt = 264 ± 27 keV; Γh = 258 ± 26 keV, Γμ = 2.44 ± 0.21 keV, and Γπ+π−J/ψ = 85.4 ± 8.7 keV; and Bh = (97.79 ± 0.15)%, Bπ+π−J/ψ = (32.3 ± 1.4)%, Bμ = (0.93± 0.08)%, respectively. Decays of J/ψ → γηc are used to determine the mass and width of the ηc using a sample of 58 M J/ψ events: Mηc = (2977.5 ± 1.0 ± 1.2) MeV and Γηc = (17.0± 3.7± 7.4) MeV. The first observation of χcJ (J=0,1,2) decays to ΛΛ is reported using ψ(2S) data collected with the BESII detector at the BEPC. The branching ratios are determined to be B(χc0 → ΛΛ) = (4.7 −1.2 ± 1.0) × 10 −4 , B(χc1 → ΛΛ) = (2.6 +1.0 −0.9 ± 0.6) × 10 −4 and B(χc2 → ΛΛ) = (3.3 −1.3 ± 0.7) × 10 . Results are compared with model predictions.