The MicroBooNE Experiment, the NuMI Absorber, and Heavy Neutral Leptons

Motivated by the recent search for a Higgs-Portal Scalar decaying inside the MicroBooNE detector, we demonstrate that the same search can be used to constrain Heavy Neutral Leptons. These are gauge-singlet fermions that interact with the Standard Model by mixing with neutrinos only and could be related to the origin of neutrino masses. By recasting the results of the MicroBooNE Collaboration's analysis, we show that, for a Heavy Neutral Lepton that mixes predominantly with muon-flavored neutrinos, previously unexplored parameter space can be excluded for masses between 30 and 150 MeV. Additionally, we make our Monte Carlo tools publicly available.
Comment: 5 pages plus references, 4 figures. Monte Carlo code available at https://github.com/kjkellyphys/muBHNL. v2: Updated references, typo in equation fixed (results unchanged), matches published version