Search for diphoton decays of an axionlike particle in radiative $J/\psi $ decays

We search for the diphoton decay of a light pseudoscalar axionlike particle, $a$, in radiative $J/\psi $ decays, using ${10}^{10}\text{}J/\psi $ events collected with the BESIII detector. We find no evidence of a signal and set upper limits at the 95% confidence level on the product branching fraction $B\left(J/\psi \to \gamma a\right)×B\left(a\to \gamma \gamma \right)$ and the axionlike particle photon coupling constant ${g}_{a\gamma \gamma }$ in the ranges of $\left(3.7–48.5\right)×{10}^{-8}$ and $\left(2.2–101.8\right)×{10}^{-4}\text{}\text{}{\mathrm{GeV}}^{-1}$, respectively, for $0.18\le {m}_{a}\le 2.85\text{}\text{}\mathrm{GeV}/{c}^{2}$. These are the most stringent limits to date in this mass region.