Search for long-lived heavy neutral leptons and Higgs portal scalars decaying in the MicroBooNE detector

Le résumé fourni par la source

We present a search for long-lived Higgs portal scalars (HPS) and heavy neutral leptons (HNL) decaying in the MicroBooNE liquid-argon time projection chamber. The measurement is performed using data collected synchronously with the neutrino beam from Fermilab's Main Injector with a total exposure corresponding to $7.01\ifmmode\times\else\texttimes\fi{}{10}^{20}$ protons on target. We set upper limits at the 90% confidence level on the mixing parameter $|{U}_{\ensuremath{\mu}4}{|}^{2}$ ranging from $|{U}_{\ensuremath{\mu}4}{|}^{2}<12.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ for Majorana HNLs with a mass of ${m}_{\mathrm{HNL}}=246\text{ }\text{ }\mathrm{MeV}$ to $|{U}_{\ensuremath{\mu}4}{|}^{2}<0.92\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ for ${m}_{\mathrm{HNL}}=385\text{ }\text{ }\mathrm{MeV}$, assuming $|{U}_{e4}{|}^{2}=|{U}_{\ensuremath{\tau}4}{|}^{2}=0$ and HNL decays into ${\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}$ pairs. These limits on $|{U}_{\ensuremath{\mu}4}{|}^{2}$ represent an order of magnitude improvement in sensitivity compared to the previous MicroBooNE result. We also constrain the scalar-Higgs mixing angle $\ensuremath{\theta}$ by searching for HPS decays into ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ final states, excluding a contour in the parameter space with lower bounds of ${\ensuremath{\theta}}^{2}<31.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ for ${m}_{\mathrm{HPS}}=212\text{ }\text{ }\mathrm{GeV}$ and ${\ensuremath{\theta}}^{2}<1.09\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ for ${m}_{\mathrm{HPS}}=275\text{ }\text{ }\mathrm{GeV}$. These are the first constraints on the scalar-Higgs mixing angle $\ensuremath{\theta}$ from a dedicated experimental search in this mass range.

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