Search for Lepton-Flavor-Violating Decays of the Neutral Kaon

Abstract

The Fermilab KTeV experiment has searched for lepton-flavor-violating decays of the ${K}_{L}$ meson in three decay modes. We observe no events in the signal region for any of the modes studied, and we set the following upper limits for their branching ratios at the 90% C.L.: $BR({K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{e}^{\ensuremath{\mp}})<7.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$; $BR({K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{e}^{\ensuremath{\mp}})<1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$; $BR({\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{e}^{\ensuremath{\mp}})<3.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$. This result represents a factor of 82 improvement in the branching ratio limit for ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{e}^{\ensuremath{\mp}}$ and is the first reported limit for ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{e}^{\ensuremath{\mp}}$.