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

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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.