Radiative decays of $h_{c}$ to the light mesons $η^{(\prime)}$: A perturbative QCD calculation

Abstract

We study the radiative decays $h_{c}\rightarrowγη^{(\prime)}$ in the framework of perturbative QCD and evaluate analytically the one-loop integrals with the light quark masses kept. Interestingly, the branching ratios $\mathcal{B}(h_{c}\rightarrowγη^{(\prime)})$ are insensitive to both the light quark masses and the shapes of $η^{(\prime)}$ distribution amplitudes. And it is noticed that the contribution of the gluonic content of $η^{(\prime)}$ is almost equal to that of the quark-antiquark content of $η^{(\prime)}$ in the radiative decays $h_{c} \rightarrow γη^{(\prime)}$. By employing the ratio $R_{h_{c}}=\mathcal{B}(h_{c}\rightarrowγη)/\mathcal{B}(h_{c}\rightarrowγη^{\prime})$, we extract the mixing angle $ϕ=33.8^{\circ}\pm2.5^{\circ}$, which is in clear disagreement with the Feldmann-Kroll-Stech result $ϕ=39.0^{\circ}\pm1.6^{\circ}$ extracted from the ratio $R_{J/ψ}$ with nonperturbative matrix elements $\langle 0\mid G^{a}_{μν}\tilde{G}^{a,μν}\midη^{(\prime)}\rangle$, but in consistent with $ϕ=33.5^{\circ}\pm0.9^{\circ}$ extracted from the asymptotic limit of the $γ^{\ast}γ-η^{\prime}$ transition form factor and $ϕ=33.9^{\circ}\pm0.6^{\circ}$ extracted from $R_{J/ψ}$ in perturbative QCD. We also briefly discuss possible reasons for the difference in the determinations of the mixing angle.