Lepton universality test with Kl2 decays at NA62 experiment

The experiment NA62 at CERN collected a large sample of K+- leptonic decays in order to perform precise test of lepton universality, by measuring the helicity suppressed ratio R_K=Gamma(K+- --> e+- nu)/Gamma(K+- --> mu+- nu). The preliminary result of the analysis based on 51089 K+ --> e+nu candidates is R_K=(2.500+-0.016)x10^{-5}, consistent with the predictions of the Standard Model.