Search for lepton number and flavour violation in $K^{+}$ and ${\pi }^0$ decays

Abstract

Searches for the lepton number violating $K^{+}\to {\pi }^{-}{\mu }^{+}{e}^{+}$ decay and the lepton flavour violating $K^{+}\to {\pi }^{+}{\mu }^{-}{e}^{+}$ and ${\pi }^0\to {\mu }^{-}{e}^{+}$ decays are reported using data collected by the NA62 experiment at CERN in $2017$-$2018$. No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level: $\mathcal{B}(K^{+}\to {\pi }^{-}{\mu }^{+}{e}^{+})<4.2\times 10^{-11}$, $\mathcal{B}(K^{+}\to {\pi }^{+}{\mu }^{-}{e}^{+})<6.6\times 10^{-11}$ and $\mathcal{B}({\pi }^0\to {\mu }^{-}{e}^{+})<3.2\times 10^{-10}$. These results improve by one order of magnitude over previous results for these decay modes.

8 pages, 4 figures

References in corpus (3)

• Measurement of the very rare $K^{+}\to {\pi }^{+}\nu \bar{\nu }$ decay
• Search for Lepton Flavor Violating Decays of the Neutral Kaon
• The integrated low-level trigger and readout system of the CERN NA62 experiment

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• Workshop summary -- Kaons@CERN 2023
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• QCD Running in Lepton Number Violating Meson and Tau Decays
• New Physics Searches at Kaon and Hyperon Factories
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• Constraining lepton flavor violating SMEFT $2q2\ell$ operators from low-energy cLFV processes
• Searches for charged-lepton-flavor violation in ${\chi }_{bJ}(1P)$ decays
• Tri-bimaximal-Cabibbo Mixing: Flavour violations in the charged lepton sector