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Intermediate hadronic meson loop contributions to $J/\psi$, $\psi^\prime \to\gamma\eta_c$ ($\gamma\eta_c^\prime$) are studied apart from the dominant M1transitions in an effective Lagrangian approach. Due to the property of theunique antisymmetric tensor coupling in $V\to VP$, the hadronic looptransitions provide explicit corrections to the M1 transition amplitudesderived from the naive "quenched" $c\bar{c}$ transitions via the coupling formfactors. This mechanism interfering with the M1 transition amplitudes naturallyaccounts for the deviations from the Godfrey-Isgur model predictions in$J/\psi$ and $\psi^\prime\to \gamma\eta_c$. It also predicts a small branchingratio of $\psi^\prime\to \gamma\eta_c^\prime$, which can be examined byexperimental measurements at BES and CLEO-c.

Hadronic loop contributions to $J/\psi$ and $\psi^\prime$ radiative decays into $\gamma\eta_c$ or $\gamma\eta_c^\prime$