Revisit the radiative decays of $J/\psi$ and $\psi'\to \gamma\eta_c (\gamma\eta_c^\prime)$

TL;DR

This paper re-examines the radiative decays of $J/ar{ ext{}}$ and $ar{ ext{}}$'s into photons and $ar{ ext{}}$ mesons using new experimental data, highlighting the importance of intermediate meson loops in understanding these processes.

Contribution

It provides a quantitative analysis of intermediate meson loop effects in radiative $J/ar{ ext{}}$ decays, incorporating recent experimental measurements within an effective Lagrangian framework.

Findings

IML effects are small in $J/ar{ ext{}}}$ decays but significant in $ar{ ext{}}$'s decays.

New data helps quantify unquenched effects in $J/ar{ ext{}}$ transitions.

Predictions are made for $ar{ ext{}}$ decays involving $ar{ ext{}}$ mesons.

Abstract

With the new measurements of $J/\psi$ and $\psi^\prime\to \gamma\eta_c \ (\gamma\eta_c^\prime)$ from CLEO and BES-III Collaboration, we re-investigate the intermediate meson loop (IML) contributions to these radiative decays in association with the quark model M1 transitions in an effective Lagrangian approach. It shows that the "unquenched" effects due to the intermediate hadron loops can be better quantified by the new data for $J/\psi\to \gamma\eta_c$. Although the IML contributions are relatively small in $J/\psi\to \gamma\eta_c$, they play a crucial role in $\psi^\prime\to \gamma\eta_c \ (\gamma\eta_c^\prime)$. A prediction for the IML contributions to $\psi(3770)\to \gamma\eta_c \ (\gamma\eta_c^\prime)$ is made. Such "unquenched" effects allow us to reach a coherent description of those three radiative transitions, and gain some insights into the underlying dynamics.