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.

Comments: Slightly modified version to appear in Phys. Lett. B