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

Abstract Using the inclusive photon spectrum based on a data sample collected at the J / ψ peak with the KEDR detector at the VEPP-4M e + e − collider, we measured the rate of the radiative decay J / ψ → γ η c as well as η c mass and width. Taking into account an asymmetric photon lineshape we obtained Γ γ η c 0 = 2.98 ± 0.18 − 0.33 + 0.15 keV , M η c = 2983.5 ± 1.4 − 3.6 + 1.6 MeV / c 2 , Γ η c = 27.2 ± 3.1 − 2.6 + 5.4 MeV .