Probing the Higgs portal at the Fermilab short-baseline neutrino experiments

The Fermilab short-baseline neutrino (SBN) experiments, MicroBooNE, ICARUS, and SBND, are expected to have significant sensitivity to light weakly coupled hidden sector particles. Here we study the capability of the SBN experiments to probe dark scalars interacting through the Higgs portal. We investigate production of dark scalars using both the Fermilab booster 8 GeV and NuMI 120 GeV proton beams, simulating kaons decaying to dark scalars and taking into account the beam line geometry. We also investigate strategies to mitigate backgrounds from beam-related neutrino scattering events. We find that SBND, with its comparatively short O(100 m) baseline, will have the best sensitivity to scalars produced from the booster, while ICARUS, with its large detector volume, will provide the best limits on off-axis dark scalar production from NuMI. The SBN experiments can provide leading tests of dark scalars with masses in the 50-350 MeV range in the near term. Our results motivate dedicated experimental searches for dark scalars and other long-lived hidden sector states at these experiments.