Search for Heavy Neutral Leptons in Electron-Positron and Neutral-Pion Final States with the MicroBooNE Detector

Abstract

We present the first search for heavy neutral leptons (HNLs) decaying into νe+e− or νπ0 final states in a liquid-argon time projection chamber using data collected with the MicroBooNE detector. The data were recorded synchronously with the NuMI neutrino beam from Fermilab’s main injector corresponding to a total exposure of 7.01 × 1020 protons on target. We set upper limits at the 90% confidence level on the mixing parameter |Uμ4|2 in the mass ranges 10 ≤ mHNL ≤ 150 MeV for the νe+e− channel and 150 ≤ mHNL ≤ 245 MeV for the νπ0 channel, assuming |Ue4|2 = |Uτ4|2 = 0. These limits represent the most stringent constraints in the mass range 35 < mHNL < 175 MeV and the first constraints from a direct search for νπ0 decays.