The NA62 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2016-2018. This sample provides sensitivities to rare decays with branching ratios as low as 10−11. Searches for the lepton number violating K+ → π−µ+e+ decay and the lepton flavour violating K+ → π+µ−e+ and π0 → µ−e+ decays are reported. No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level. These results improve by one order of magnitude over previous results for these decay modes.
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