Hadronic loop contributions to J/ψ and ψ′ radiative decays into γηc or γηc′

Intermediate hadronic meson loop contributions to J/ψ, ψ′→γηc (γηc′) are studied apart from the dominant M1 transitions in an effective Lagrangian approach. Due to the property of the unique antisymmetric tensor coupling in V→VP, the hadronic loop transitions provide explicit corrections to the M1 transition amplitudes derived from the naive “quenched” cc¯ transitions via the coupling form factors. This mechanism interfering with the M1 transition amplitudes naturally accounts for the deviations from the Godfrey-Isgur model predictions in J/ψ and ψ′→γηc. It also predicts a small branching ratio of ψ′→γηc′, which can be examined by experimental measurements at BES and CLEO-c.