Abstract
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.
Highlights
The branching fraction for semileptonic decays of charged and neutral kaons together with the lifetime measurements are used to determine the |V us| element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix
The K S → π μν decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement
We present a measurement of the K S → π μν branching fraction performed by the KLOE experiment at the DA NE φ–factory of the Frascati National Laboratory based on an integrated luminosity of 1.6 fb−1
Summary
The branching fraction for semileptonic decays of charged and neutral kaons together with the lifetime measurements are used to determine the |V us| element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix. Given the lack of pure high-intensity K S meson beams contrary to the case of K ± and K L mesons, the K S → π eν decay provides the least precise determination of |V us|, and the branching fraction B(K S → π μν) has not yet been measured. Measurement of this decay mode allows an independent determination of |V us| and to extend the test of lepton-flavour universality to K S semileptonic decays by comparison with the expected value of (4.69 ± 0.06) × 10−4 [4] derived from B(K S → π eν). The branching fraction is extracted normalising the number of K S → π μν events to the number of K S → π +π − events recorded in the same dataset
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