Understanding the radiative decays of vector charmonia to light pseudoscalar mesons

We show that the newly measured branching ratios of vector charmonia (J/ψ, ψ′ and ψ(3770)) into γP, where P stands for light pseudoscalar mesons π0, η, and η′, can be well understood in the framework of vector meson dominance (VMD) in association with the ηc-η(η′) mixings due to the axial gluonic anomaly. These two mechanisms behave differently in J/ψ and ψ′→γP. A coherent understanding of the branching ratio patterns observed in J/ψ(ψ′)→γP can be achieved by self-consistently including those transition mechanisms at hadronic level. The branching ratios for ψ(3770)→γP are predicted to be rather small.