Search for a low-mass Higgs boson ($A^0$) at BABAR

The BABAR Collaboration has performed three searches for a light Higgs boson, $A^0$, in radiative Upsilon ($\mathrm{{\rm Y}}$) decays: $\mathrm{{\rm Y}}(3S)\to \gamma A^0$, $A^0\to {\tau }^{+}{\tau }^{-}$; $\mathrm{{\rm Y}}(nS)\to \gamma A^0$, $A^0\to {\mu }^{+}{\mu }^{-}$ ($n=2,3$); and $\mathrm{{\rm Y}}(3S)\to \gamma A^0$, $A^0\to$ invisible. Such a Higgs boson ($A^0$) appears in the Next-to-Minimal Supersymmetric extensions of the Standard Model, where a light CP-odd Higgs boson couples strongly to $b$-quarks. The searches are based on data samples that consist of $122\times 10^6$ $\mathrm{{\rm Y}}(3S)$ and $99\times {10}^6$ $\mathrm{{\rm Y}}(2S)$ decays, collected by the BABAR detector at the SLAC National Accelerator Laboratory. The searches reveal no evidence for an $A^0$, and product of branching fractions upper limits, at 90% C.L., of $(1.5-16)\times {10}^{-5}$, $(0.44-44)\times {10}^{-6}$, and $(0.7-31)\times {10}^{-6}$ were obtained for these searches, respectively. Also, we set the upper limits $\mathcal{B}({\eta }_b\to {\tau }^{+}{\tau }^{-})<8$ and $\mathcal{B}({\eta }_b\to {\mu }^{+}{\mu }^{-})<0.9$.