Search for di-photon decays of an axion-like particle in radiative J/ψ decays

We search for the di-photon decay of a light pseudoscalar axion-like particle, a, in radiative J/ψ decays, using 10 billion J/ψ 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(J/ψ → γ a) × B(a → γ γ) and the axion-like particle photon coupling constant ga γ γ in the ranges of (3.7-48.5) × 10⁻⁸ and (2.2 -101.8)× 10⁻⁴ GeV⁻¹, respectively, for 0.18 ≤ mₐ ≤ 2.85 GeV/c². These are the most stringent limits to date in this mass region.