Search for a Higgs portal scalar decaying to electron-positron pairs in the MicroBooNE detector

TL;DR

This paper searches for a Higgs portal scalar decaying to electron-positron pairs in the MicroBooNE detector, setting limits on scalar-Higgs mixing and excluding certain model parameters related to rare kaon decays.

Contribution

It presents the first search for a Higgs portal scalar in the MicroBooNE detector, providing new constraints on scalar-Higgs mixing angles and model parameters.

Findings

Observed one candidate event with background prediction of 1.9±0.8.

Set upper limits on scalar-Higgs mixing angle of (3.3-4.6)×10^{-4}.

Excluded model parameters related to KOTO's excess at 95% confidence level.

Abstract

We present a search for the decays of a neutral scalar boson produced by kaons decaying at rest, in the context of the Higgs portal model, using the MicroBooNE detector. We analyze data triggered in time with the Fermilab NuMI neutrino beam spill, with an exposure of $1.93\times10^{20}$ protons on target. We look for monoenergetic scalars that come from the direction of the NuMI hadron absorber, at a distance of 100 m from the detector, and decay to electron-positron pairs. We observe one candidate event, with a Standard Model background prediction of $1.9\pm0.8$. We set an upper limit on the scalar-Higgs mixing angle of $\theta<(3.3-4.6)\times10^{-4}$ at the 95% confidence level for scalar boson masses in the range $(100-200)$ MeV$/c^2$. We exclude at the 95% confidence level the remaining model parameters required to explain the central value of a possible excess of $K^0_L\rightarrow\pi^0\nu\bar{\nu}$ decays reported by the KOTO collaboration. We also provide a model-independent limit on a new boson $X$ produced in $K\rightarrow\pi X$ decays and decaying to $e^+e^-$.