Lepton flavour universality and lepton flavour conservation tests in kaon decays at CERN

A precision measurement of the ratio of the rates of kaon leptonic decays K± → e± v and K± → μ±v with the full minimum bias data sample collected with low intensity 75 GeV/c beam by the NA62 experiment at CERN in 2007-2008 is reported. The result, obtained by analyzing 150,000 reconstructed K ± → e± v candidates with 11% background contamination, has a record precision of 0.4% and is in agreement with the Standard Model expectation. An improved upper limit on the rate of the lepton number violating decay K± → π±μ ±μ± from the NA48/2 experiment, which probes the resonant enhancement of the rate in the presence of heavy Majorana neutrinos in the 100 MeV range, is also reported. The prospects for the searches of lepton number and flavour violating decays of the charged kaon with an improved sensitivity down to 10-12 during the forthcoming main phase of the NA62 experiment are discussed. © Copyright owned by the author(s)