Searches for lepton number violating K+ → π−(π0)e+e+ decays

Abstract

Searches for lepton number violating K + → π − e + e + and K + → π − π 0 e + e + decays have been performed using the complete dataset collected by the NA62 experiment at CERN in 2016–2018. Upper limits of 5.3 × 10 − 11 and 8.5 × 10 − 10 are obtained on the decay branching fractions at 90% confidence level. The former result improves by a factor of four over the previous best limit, while the latter result represents the first limit on the K + → π − π 0 e + e + decay rate.