Searches for lepton flavour and lepton number violation in kaon decays

TL;DR

This paper reports on searches for lepton flavor and number violation in kaon decays, including a precise measurement of decay rate ratios and improved limits on lepton number violating processes, advancing the understanding of rare kaon decays.

Contribution

It provides the first sub-percent measurement of the ratio RK and sets new upper limits on lepton number violating kaon decays, improving constraints on new physics models.

Findings

Precise measurement of RK with sub-percent accuracy.

Improved upper limit on lepton number violating decay rate.

Enhanced constraints on theories beyond the Standard Model.

Abstract

Searches for lepton flavour and lepton number violation in kaon decays by the NA48/2 and NA62 experiments at CERN are presented. A new measurement of the helicity suppressed ratio of charged kaon leptonic decay rates $RK=BR(Ke2)/BR(Kmu2) to sub-percent relative precision is discussed. An improved upper limit on the lepton number violating K+- --> pi-+mu+-mu+- decay rate is also presented.