Measurement of the KS→ πeν branching fraction with the KLOE experiment

Abstract

The ratio mathcal{R} = Γ(KS→ πeν)/Γ(KS→ π+π−) has been measured with a sample of 300 million KS mesons produced in ϕ → KLKS decays recorded by the KLOE experiment at the DAΦNE e+e− collider. KS→ πeν events are selected by a boosted decision tree built with kinematic variables and time-of-flight measurements. Data control samples of KL→ πeν decays are used to evaluate signal selection efficiencies. With 49647±316 signal events we measure mathcal{R} = (1.0421 ± 0.0066stat± 0.0075syst) × 10−3. The combination with our previous measurement gives mathcal{R} = (1.0338 ± 0.0054stat± 0.0064syst) × 10−3. From this value we derive the branching fraction mathcal{B} (KS→ πeν) = (7.153 ± 0.037stat± 0.044syst) × 10−4 and f+(0)|Vus| = 0.2170 ± 0.009.