Riccardo Fantechi (Sezione di Pisa (IT))
A lepton universality test by measurement of the helicity suppressed ratio RK of leptonic decay rates of the charged kaon has been performed by the NA62 experiment. A precision measurement of the ratio RK of the rates of kaon leptonic decays K+- to e+- nu and K+- to mu+- nu with the full minimum bias data sample collected with low intensity 75 GeV/c beam by the NA62 experiment at CERN in 2007-2008 is reported. The result, obtained by analyzing ~150,000 reconstructed K+- to e+- nu candidates with 11% background contamination, has a record precision of 0.4% and is in agreement with the Standard Model expectation. The record accuracy of 0.4% constrains the parameter space of new physics models with extended Higgs sector, a fourth generation of quarks and leptons or sterile neutrinos.
Cristina Lazzeroni (University of Birmingham (GB))