Test of Lepton Flavour Universality in K+ --> l+nu Decays
  A precision test of lepton flavour universality has been performed by measuring the ratio RK of kaon leptonic decay rates K+ --> e+nu and K+ --> mu+nu in a sample of 59813 reconstructed K+ --> e+nu candidates with (8.71 +- 0.24)% background contamination. The result RK = (2.487 +- 0.013) * 10^{-5} is in agreement with the Standard Model expectation. 
C. Lazzeroni et al. (NA62 collaboration)
hep-ex