Revisit the radiative decays of and J/ψ and ψ' → γηc(γη'c).

With the new measurements of J/ψ and ψ' → γηc(γη'c) from the CLEO and BES-III collaboration, we reinvestigate the intermediate meson loop (IML) contributions to these radiative decays in association with the quark model M1 transitions in an effective Lagrangian approach. It shows that the "unquenched" effects due to the intermediate hadron loops can be better quantified by the new data for J/ψ → γηc. Although the IML contributions are relatively small in J/ψ → γηc, they play a crucial role in ψ' → γηc(γη'c). A prediction for the IML contributions to ψ(3770) → γηc(γη'c) is made. Such unquenched effects allow us to reach a coherent description of those three radiative transitions, and gain some insights into the underlying dynamics. [ABSTRACT FROM AUTHOR]