Abstract
A precision measurement of the ratio RK of the rates of kaon leptonic decays K±→e±ν and K±→μ±ν with the full data sample collected by the NA62 experiment at CERN in 2007–2008 is reported. The result, obtained by analysing ∼150000 reconstructed K±→e±ν candidates with 11% background contamination, is RK=(2.488±0.010)×10−5, in agreement with the Standard Model expectation.
Highlights
The decays of pseudoscalar mesons to light leptons are helicity suppressed in the Standard Model (SM) due to the V−A structure of the charged current coupling
The SM predictions for Pl2 decay rates are affected by hadronic uncertainties via the decay constant, ratios of decay rates of the same parent meson do not depend on fP and can be computed very precisely
The present analysis extends to the whole data sample and involves several improvements on the estimation of backgrounds and systematic uncertainties
Summary
The decays of pseudoscalar mesons to light leptons are helicity suppressed in the Standard Model (SM) due to the V−A structure of the charged current coupling. Within extensions of the SM involving two Higgs doublets, RK is sensitive to lepton flavour violating effects induced by loop processes with the charged Higgs boson (H±) exchange [2]. RK is sensitive to the neutrino mixing parameters within SM extensions involving a fourth generation of quarks and leptons [5] or sterile neutrinos [6]. Measurements of RK have recently been reported by the KLOE [7] and NA62 [8] experiments. An improved measurement based on the full dedicated data sample collected by the NA62 experiment in 2007–2008 and superseding the earlier result [8] is reported here
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