Search for a $CP$-odd light Higgs boson in $J/\psi \to \gamma A^0$

TL;DR

This study searches for a hypothetical $CP$-odd light Higgs boson in $J/A$ radiative decays using a large dataset, setting upper limits on its production and decay probabilities, and improving upon previous measurements.

Contribution

First search for a $CP$-odd light Higgs in $J/A$ decays with significantly improved upper limits, constraining new physics models beyond the Standard Model.

Findings

No evidence for $A^0$ production was observed.

Set upper limits on the product branching fraction in the range of $(1.2-778.0) imes 10^{-9}$.

Measurement improves previous results by a factor of 6-7.

Abstract

Using $J/\psi$ radiative decays from 9.0 billion $J/\psi$ events collected by the BESIII detector, we search for di-muon decays of a $CP$-odd light Higgs boson ($A^0$), predicted by many new physics models beyond the Standard Model, including the Next-to-Minimal Supersymmetric Standard Model. No evidence for the $CP$-odd light Higgs production is found, and we set $90\%$ confidence level upper limits on the product branching fraction $\mathcal{B}(J/\psi \to \gamma A^0)\times \mathcal{B}(A^0 \to \mu^+\mu^-)$ in the range of $(1.2-778.0)\times 10^{-9}$ for $0.212 \le m_{A^0} \le 3.0$ GeV/$c^2$. The new measurement is a 6-7 times improvement over our previous measurement, and is also slightly better than the BaBar measurement in the low-mass region for $\tan \beta =1$.