Search for long-lived heavy neutral leptons and Higgs portal scalars decaying in the MicroBooNE detector Abratenko, P. García Gámez, Diego Microboone Collaboration ACKNOWLEDGMENTS This document was prepared by the MicroBooNE Collaboration using the resources of the Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy, Office of Science, HEP User Facility. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359. MicroBooNE is supported by the following: the U.S. Department of Energy, Office of Science, Offices of High Energy Physics and Nuclear Physics; the U.S. National Science Foundation; the Swiss National Science Foundation; the Science and Technology Facilities Council (STFC), part of the United Kingdom Research and Innovation; the Royal Society (United Kingdom); and The European Union’s Horizon 2020 Marie Skłodowska-Curie Actions. Additional support for the laser calibration system and cosmic-ray tagger was provided by the Albert Einstein Center for Fundamental Physics, Bern, Switzerland. For the purpose of open access, the authors have applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising from this submission. We also acknowledge the contributions of technical and scientific staff to the design, construction, and operation of the MicroBooNE detector as well as the contributions of past collaborators to the development of MicroBooNE analyses, without whom this work would not have been possible. We particularly acknowledge the many contributions of Salvatore Davide Porzio to developing this research direction on MicroBooNE. 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 7.01×1020 protons on target. We set upper limits at the 90% confidence level on the mixing parameter |Uμ4|2 ranging from |Uμ4|2<12.9×10−8 for Majorana HNLs with a mass of mHNL=246  MeV to |Uμ4|2<0.92×10−8 for mHNL=385  MeV, assuming |Ue4|2=|Uτ4|2=0 and HNL decays into μ±π∓ pairs. These limits on |Uμ4|2 represent an order of magnitude improvement in sensitivity compared to the previous MicroBooNE result. We also constrain the scalar-Higgs mixing angle θ by searching for HPS decays into μ+μ− final states, excluding a contour in the parameter space with lower bounds of θ2<31.3×10−9 for mHPS=212  GeV and θ2<1.09×10−9 for mHPS=275  GeV. These are the first constraints on the scalar-Higgs mixing angle θ from a dedicated experimental search in this mass range. 2023-01-12T12:32:06Z 2023-01-12T12:32:06Z 2022-11-28 journal article P. Abratenko et al. (MicroBooNE Collaboration1) Search for long-lived heavy neutral leptons and Higgs portal scalars decaying in the MicroBooNE detector. Phys. Rev. D 106, 092006 [https://doi.org/10.1103/PhysRevD.106.092006] https://hdl.handle.net/10481/78953 10.1103/PhysRevD.106.092006 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional American Physical Society