Lepton universality test with K+ --> l+ nu decays

The NA62 experiment at CERN collected a large sample of $K^+\to e^+ν$ decays during a dedicated run in 2007, which allows a precise test of lepton universality by measurement of the helicity suppressed ratio $R_K = Γ(K^+\to e^+ν)/Γ(K^+\toμ^+ν)$. The preliminary result of the analysis of a partial data sample of 51089 $K^+\to e^+ν$ candidates is $R_K=(2.500\pm0.016)\times10^{-5}$, consistent with the Standard Model expectation.

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