First search for $K^{+}\to \ddot{I}{€}^0\ddot{I}€\hat{I}¼e$ decays

Abstract

The first search for the lepton number violating decay $K^{+}\to \ddot{I}{€}^0\ddot{I}{€}^{-}\hat{I}{¼}^{+}{e}^{+}$ and lepton flavour violating decays $K^{+}\to \ddot{I}{€}^0\ddot{I}{€}^{+}\hat{I}{¼}^{-}{e}^{+}$, $K^{+}\to \ddot{I}{€}^0\ddot{I}{€}^{+}\hat{I}{¼}^{+}{e}^{-}$ has been performed using a dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of $2.9\times 10^{-10}$, $3.1\times 10^{-10}$ and $5.0\times 10^{-10}$, respectively, are obtained at 90% CL for the branching ratios of the three decays on the assumption of uniform phase-space distributions.

Updated version, accepted for publication in Physics Letters B