The new K_S →π e ν branching fraction measurement at KLOE

A new measurement of the branching fraction for the decay K_S →π e ν is presented, based on a sample of 300 million K_S mesons recorded by the KLOE experiment at the DAΦNE e^+e^- collider. A two-step signal selection strategy is used, exploiting first kinematic variables and then time-of-flight measurements. Data control samples of K_S →π e ν decays are used to evaluate signal selection efficiencies. Normalizing the selected sample to the number of K_S →π^+ π^- decay events the result for the branching fraction is B(K_S →π e ν)=(7.211 ± 0.046 ± 0.052)× 10^-4. The combination with our previous measurement gives B(K_S →π e ν)=(7.153 ± 0.037 ± 0.043)× 10^-4 =(7.153 ± 0.057)× 10^-4. From this value we derive f^+(0)|Vus|=0.2170 ± 0.0009.