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arXiv · 2507.07345

Search for heavy neutral leptons in $\pi^+$ decays to positrons

NA62 Collaboration
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Abstract

A search for heavy neutral lepton ($N$) production in $\pi^+\to e^+ N$ in-flight decays using data collected by the NA62 experiment at CERN in 2017-2024 is reported. Upper limits for the extended neutrino mixing matrix element $|U_{e4}|^2$ are established at the level of $10^{-8}$ for heavy neutral leptons with mass in the range 95-126 $MeV/c^2$ and lifetime exceeding 50 ns.

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NA62 Collaboration. 2025-07-10. Search for heavy neutral leptons in $\pi^+$ decays to positrons. https://doi.org/10.1016/j.physletb.2025.140119

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