Measurements of the mass and full-width of the ηc meson

Abstract In a sample of 58 million J/ψ events collected with the BES II detector, the process J/ψ→γηc is observed in five different decay channels: γK+K−π+π−, γπ+π−π+π−, γK±K0Sπ∓ (with K0S→π+π−), γφφ (with φ→K+K−) and γp p . From a combined fit of all five channels, we determine the mass and full-width of the ηc to be m η c =2977.5±1.0 ( stat. )±1.2 ( syst. )  MeV /c 2 and Γ η c =17.0±3.7 ( stat. )±7.4 ( syst. )  MeV /c 2 .