Hadronic loop correction of charmonium decays

Recently, the effect of next leading order correction from intermediate hadronic loops to the charmonium decays has been widely studied. However, the coupling constants of the charmonium multiplets and heavy mesons cannot be directly measured from experiments. In this talk, we will present the investigation of hadronic loop correction to both hadronic decays and radiative decays of the lowest excited states of charmonia and try to extract the reasonable coupling constants.