Search for Low-Mass Dark-Sector Higgs Bosons

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 $516{\mathrm{fb}}^{-1}$ 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.

Figure 1

Distribution of the largest mass difference between the three dark photon candidates ($\Delta M$) versus the average dark photon mass ($m_{A^{\prime }}$) after all other selection criteria are applied for the $2e4\pi$ 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 data set (open squares). The Monte Carlo predictions for $m_{h^{\prime }}=3.0\mathrm{GeV}$ and $m_{A^{\prime }}=0.5\mathrm{GeV}$ are displayed as plain circles. The signal region for the $2e4\pi$ mode is delimited by the dashed line.

Figure 2

Distribution of dark photon mass ($m_{A^{\prime }}$) versus the dark Higgs mass ($m_{h^{\prime }}$) for the final data sample. Three entries are plotted for each event, corresponding to the possible assignments of the decay $h^{\prime }\to A^{\prime }{A}^{\prime }$.

Figure 3

Upper limit (90% CL) on the $e^{+}{e}^{-}\to A^{\prime }{h}^{\prime }$, $h^{\prime }\to A^{\prime }{A}^{\prime }$ cross-section as a function of the dark photon and dark Higgs masses. The limits in the $\omega$- and $\varphi$-mesons regions are orders of magnitude larger than the average limits and the corresponding regions (horizontal bands centered around $m_{A^{\prime }}\sim 0.78\mathrm{GeV}$ and $m_{A^{\prime }}\sim 1.04\mathrm{GeV}$) are masked to avoid overflow.

Figure 4

Upper limit (90% CL) on the product ${\alpha }_D{ϵ}^2$ 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).