Measurement of J/ψ→γηcJ/ψ→γηc decay rate and ηcηc parameters at KEDR

Using the inclusive photon spectrum based on a data sample collected at the J/ψJ/ψ peak with the KEDR detector at the VEPP-4M e+e−e+e− collider, we measured the rate of the radiative decay J/ψ→γηcJ/ψ→γηc as well as ηcηc mass and width. Taking into account an asymmetric photon lineshape we obtained Γγηc0=2.98±0.18−0.33+0.15keV, Mηc=2983.5±1.4−3.6+1.6MeV/c2, Γηc=27.2±3.1−2.6+5.4MeV.