Based on a sample of 300 million KS mesons produced in ϕ→KLKS decays recorded by the KLOE experiment at the DAΦNE e+e collider we have measured the branching fraction for the decay KS→πμν. The KS mesons are identified by the interaction of KL mesons in the detector. The KS→πμν decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of KL→πμν decays. A fit to the reconstructed muon mass distribution finds 7223±180 signal events. Normalising to the KS→π+π decay events the result for the branching fraction is B(KS→πμν)=(4.56±0.11stat±0.17syst)×10−4. It is the first measurement of this decay mode and the result allows an independent determination of |Vus| and a test of the lepton-flavour universality.

Язык оригиналаанглийский
Номер статьи135378
Число страниц8
ЖурналPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
СостояниеОпубликовано - 10 мая 2020

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