Lepton flavour universality test at the CERN NA62 experiment

A precision test of lepton universality by measurement of the ratio RK of K+→e+ν to K+→μ+ν decay rates was performed using a sample of 59963 K+→e+ν candidates with 8.8% background contamination collected by the CERN NA62 experiment. The result RK=(2.486±0.013)×10−5 is in agreement with the Standard Model expectation.