A Search for Dark Higgs Bosons

TL;DR

We search for a light dark Higgs boson in the Higgs-strahlung channel $e^+e^- \rightarrow A' h', h' \rightarrow A' A'$ using a data sample of about $516\ \mathrm{fb}^{-1}$ collected with the BABAR detector. The analysis covers $0.8 < m_{h'} < 10\ \mathrm{GeV}$ and $0.25 < m_{A'} < 3\ \mathrm{GeV}$ with $m_{h'} > 2 m_{A'}$, employing both exclusive and inclusive final states to reconstruct dark photons. No significant signal is observed, and 90% CL upper limits are set on the production cross-section, typically in the range $10-100\ \mathrm{ab}$, which translate to constraints on the product $\alpha_D \epsilon^2$ as a function of the dark-photon and dark-Higgs masses. Assuming $\alpha_D = \alpha$, the inferred mixing parameter $\epsilon$ reaches the $10^{-4}-10^{-3}$ range, surpassing current bounds and extending sensitivity to a GeV-scale hidden sector with an Abelian Higgs boson.

Abstract

Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs boson using 516 fb-1 of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the Standard Model-dark sector mixing angle and the dark sector coupling constant.

Figures (4)

• Figure 1: Distribution of the largest mass difference between the three dark photon candidates ($\Delta M$) versus the average dark photon mass ($m_{A'}$) after all other selection criteria are applied for the $2e 4\pi$ final state. The data are shown for opposite-sign combinations from the optimization sample (plain squares) as well as an additional background estimation, described later, of same-sign combinations from the full dataset (open squares). The Monte Carlo predictions for $m_{h'}=3.0 \mathrm{\,Ge V}\xspace$ and $m_{A'} = 0.5 \mathrm{\,Ge V}\xspace$ are displayed as plain circles. The signal region for the $2e 4\pi$ mode is delimited by the dashed line.
• Figure 2: Distribution of dark photon mass ($m_{A'}$) versus the dark Higgs mass ($m_{h'}$) for the final data sample. Three entries are plotted for each event, corresponding to the possible assignments of the decay $h' \rightarrow A' A'$.
• Figure 3: Upper limit (90% CL) on the $e^+e^- \rightarrow A' h', h' \rightarrow A' A'$ cross-section as a function of the dark photon and dark Higgs masses. The limits in the $\omega$- and $\phi$-mesons regions are orders of magnitude larger than the average limits and the corresponding regions (horizontal bands centered around $m_{A'} \sim 0.78 \mathrm{\,Ge V}\xspace$ and $m_{A'} \sim 1.04 \mathrm{\,Ge V}\xspace$) are masked to avoid overflow.
• Figure 4: Upper limit (90% CL) on the product $\alpha_D \epsilon^2$ as a function of the dark photon mass for selected values of dark Higgs boson masses (top) and as a function of the dark Higgs boson mass for selected values of dark photon masses (bottom).