Lepton flavour universality and conservation tests in Kaon decays at CERN

Abstract

A test of lepton flavour conservation in kaon rare decays by the NA48/2 experiment at CERN SPS is presented. The improved upper limit on the rate of the lepton number violating decay K ± → π ∓ μ ± μ ± is established with the data sample collected in 2003–2004. A precision test of lepton flavour universality in kaon rare decays by the successor NA62 experiment at CERN SPS is reported. The helicity suppressed ratio R K = Γ(K ± → e ± ν )/Γ(K ± → μ ± ν ) is measured with a 0.4% precision using the data sample collected in 2007–2008 and is consistent with the prediction of the Standard Model. The main goal of the NA62 experiment is to measure the branching ratio of the ultra-rare K + → π + ν ν decay with 10% accuracy. This will be achieved by collecting ∼ 1013 K + decays in the fiducial volume. The NA62 estimated sensitivities to rare and forbidden decays of K + and π 0 , including lepton flavour and number violating modes, and the NA62 potential to improve on several experimental limits are discussed.