New Limit on Muon and Electron Lepton Number Violation from $K^0_L \to \mu^\pm e^\mp$ Decay

TL;DR

This paper reports a new upper limit on the rare decay $K^0_L o \mu^\pm e^\mp$, significantly constraining theories that predict lepton number violation in kaon decays.

Contribution

The study provides the most sensitive experimental upper limit to date on the lepton number violating decay of $K^0_L$, improving constraints on new physics models.

Findings

No events observed for the decay process.

90% confidence level upper limit on branching fraction is $4.7 imes 10^{-12}$.

Results tighten constraints on lepton number violation theories.

Abstract

The most sensitive experiment to date to search for the muon and electron lepton number violating decay $K^0_L \to \mu^\pm e^\mp$ has detected no events consistent with this process. Based on this result, the 90% confidence level upper limit on the branching fraction is $B(K^0_L \to \mu^\pm e^\mp) < 4.7\times10^{-12}$.