Search for di-muon decays of a light scalar Higgs boson in radiative Y(1S) decays

TL;DR

This study searches for a light scalar Higgs boson decaying into muon pairs in radiative upsilon decays, using large datasets, but finds no evidence and sets upper limits on the decay probabilities and coupling strengths.

Contribution

First search for di-muon decays of a light Higgs in radiative upsilon decays, providing new upper limits on branching fractions and coupling constants.

Findings

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

Set upper limits on branching fractions between $0.28$ and $9.7 imes 10^{-6}$.

Combined results constrain the effective coupling $f_{b}$ of the $b$-quark to $A^0$.

Abstract

We search for di-muon decays of a low-mass Higgs boson ($A^0$) in the fully reconstructed decay chain of $\Upsilon(2S,3S) \to \pipi\Upsilon(1S)$, $\Upsilon(1S) \to \g A^0$, $A^0 \to \mumu$. The $A^0$ is predicted by several extensions of the Standard Model (SM), including the Next-to-Minimal Supersymmetric Standard Model (NMSSM). NMSSM introduces a \CP-odd light Higgs boson whose mass could be less than 10 \gevcc. The data samples used in this analysis contain $92.8 \times 10^6$ $\Upsilon(2S)$ and $116.8 \times 10^6$ $\Upsilon(3S)$ events collected by the \babar\ detector. The $\Upsilon(1S)$ sample is selected by tagging the pion pair in the $\Upsilon(2S, 3S) \to \pi^+\pi^-\Upsilon(1S)$ transitions. We find no evidence for $A^0$ production and set 90% confidence level (C.L.) upper limits on the product branching fraction $\mathcal{B}(\Upsilon(1S) \to \g A^0) \times \mathcal{B}(A^0 \to \mumu)$ in the range of $(0.28 - 9.7)\times 10^{-6}$ for $0.212 \le m_{A^0} \le 9.20$ \gevcc. We also combine our results with previous \babar\ results of $\Upsilon(2S,3S) \to \g A^0$, $A^0 \to \mumu$ to set limits on the effective coupling ($f_{\Upsilon}$) of the \b-quark to the $A^0$, $f_{\Upsilon}^2 \times \mathcal{B}(A^0 \to \mumu)$, at the level of $(0.29 - 40)\times 10^{-6}$ for $0.212 \le m_{A^0} \le 9.2$ GeV/$c^2$.