Search for a light CP-odd Higgs boson in the radiative decays of J/psi

We search for a light Higgs boson $A^0$ in the fully reconstructed decay chain of $J\mathrm{/}\psi \to \gamma A^0$, $A^0\to {\mu }^{+}{\mu }^{-}$ using $(225.0\pm 2.8)\times {10}^6$ $J\mathrm{/}\psi$ events collected by the BESIII experiment. The $A^0$ is a hypothetical CP-odd light Higgs boson predicted by many extensions of the Standard Model including two spin-0 doublets plus an extra singlet. We find no evidence for $A^0$ production and set $90\mathrm{\%}$ confidence-level upper limits on the product branching fraction $$\mathcal{B}$(J/\psi \rightarrow \gamma A^0) \times $\mathcal{B}$(A^0 \rightarrow \mu^+\mu^-)$intherangeof$(2.8-495.3)\times 10^{-8}$for$0.212 \le m_{A^0} \le 3.0$GeV\mathrm{/}c$^2$\mathrm{.}Thenewlimitsare$5$ times below our previous results, and the nature of the $A^0$ is constrained to be mostly singlet.