Heavy neutral leptons below the kaon mass at hodoscopic neutrino detectors
Carlos A. Argüelles (Department of Physics and Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge, Massachusetts 02138, USA); Nicolò Foppiani (Department of Physics and Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge, Massachusetts 02138, USA); Matheus Hostert (Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2J 2W9, Canada, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA, William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA)
Heavy neutral leptons () below the kaon mass are severely constrained by cosmology and lab-based searches for their decays in flight. If interacts via an additional force, decays are enhanced and cosmological limits can be avoided. We show that the T2K and MicroBooNE neutrino experiments provide the best limits on the mixing of with muon neutrinos, outperforming past-generation experiments, previously thought to dominate. We constrain models with electromagnetically decaying and long-lived , such as in a transition-magnetic-moment portal and in a leptophilic axionlike particle portal, invoked to explain the MiniBooNE excess. By considering these models as representative examples, our results show that explanations of the MiniBooNE excess that involve pairs from long-lived particles are in tension with T2K, PS191, and MicroBooNE data. Similarly, these searches also constrain MiniBooNE explanations based on single photons due to the associated decay mode via a virtual photon.
