Search for heavy neutral leptons in electron-positron and neutral-pion final states with the MicroBooNE detector

Blake, A. and Devitt, A. and Gu, L. and Mawby, I. and Nowak, J. and Patel, N. and Pophale, I. and Thorpe, C. (2024) Search for heavy neutral leptons in electron-positron and neutral-pion final states with the MicroBooNE detector. Physical review letters, 132 (4): 041801. ISSN 1079-7114

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Abstract

We present the first search for heavy neutral leptons (HNL) decaying into $\nu e^+e^-$ or $\nu\pi^0$ 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 $7.01 \times 10^{20}$ protons on target. We set upper limits at the $90\%$ confidence level on the mixing parameter $\lvert U_{\mu 4}\rvert^2$ in the mass ranges $10\le m_{\rm HNL}\le 150$ MeV for the $\nu e^+e^-$ channel and $150\le m_{\rm HNL}\le 245$ MeV for the $\nu\pi^0$ channel, assuming $\lvert U_{e 4}\rvert^2 = \lvert U_{\tau 4}\rvert^2 = 0$. These limits represent the most stringent constraints in the mass range $35