Determination of the radiative decay width of the ηc meson

Abstract An analysis of the reaction γ → η c was performed in five different decay channels of the η c : K S 0 K ± π ∓ , K + K − π + π − , 2 π + 2 π − , φφ and 2 K + 2 k − . A value Γ γγ ( η c ) = (11.3±4.2) keV was obtained for the radiative decay width by combining the results from the first four channels. Using our result on the two-photon width we also determined the branching ratio for the decay η c → 2 K + 2 K − .