An anlaysis on $J\mathrm{/}\psi \to {\pi }^0{\gamma }^{\ast }$ within resonance chiral theory

In this study, we analyze the first measurement of the electron-positron invariant mass spectrum in $J\mathrm{/}\psi \to {\pi }^0{e}^{+}{e}^{-}$ by BESIII, using the framework of resonance chiral theory. Our results indicate that both strong interaction and electromagnetic transition are essential to accurately describe the data. We obtain the ${\pi }^0$ transition form factor for $J\mathrm{/}\psi \to {\pi }^0{\gamma }^{\ast }$ and the corresponding decay branching ratios for $J\mathrm{/}\psi \to {\pi }^0{l}^{+}{l}^{-}$. The decay process $J\mathrm{/}\psi \to {\pi }^{0}V$ is also examined. It is found that $J\mathrm{/}\psi \to {\pi }^0{\rho }^0$ is dominated by the strong interaction, while the other two channels, $J\mathrm{/}\psi \to {\pi }^0\omega$ and ${\pi }^0\phi$, arise primarily from electromagnetic transitions.