MEASUREMENT OF $\mathcal{B}(J/\psi\to \eta_{{\rm c}}\gamma)$ AT KEDR

Abstract

We present a study of the inclusive photon spectrum from 6.3 million J/ψ decays collected with the KEDR detector at the VEPP-4M e+e- collider. We measure the branching fraction of the radiative decay J/ψ → ηcγ, ηc width and mass. Taking into account an asymmetric photon line shape we obtain: Mηc = (2978.1 ± 1.4 ± 2.0) MeV/c2, Γηc = (43.5 ± 5.4 ± 15.8) MeV, [Formula: see text].