Understanding the radiative decays of vector charmonia to light pseudoscalar mesons

Abstract

We show that the newly measured branching ratios of vector charmonia ($J/\psi$, $\psi^\prime$ and $\psi(3770))$ into $\gamma P$, where $P$ stands for light pseudoscalar mesons $\pi^0$, $\eta$, and $\eta^\prime$, can be well understood in the framework of vector meson dominance (VMD) in association with the $\eta_c$-$\eta(\eta^\prime)$ mixings due to the axial gluonic anomaly. These two mechanisms behave differently in $J/\psi$ and $\psi^\prime\to \gamma P$. A coherent understanding of the branching ratio patterns observed in $J/\psi(\psi^\prime)\to \gamma P$ can be achieved by self-consistently including those transition mechanisms at hadronic level. The branching ratios for $\psi(3770)\to\gamma P$ are predicted to be rather small.