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A new measurement of the branching fraction for the decay KS e is presented, based on a sample of 300 million KS mesons recorded by the KLOE experiment at the DANE 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 KS e decays are used to evaluate signal selection efficiencies. Normalizing the selected sample to the number of KS ^+ ^- decay events the result for the branching fraction is B (KS e) = (7. 211 0. 046 0. 052) 10^-4. The combination with our previous measurement gives B (KS e) = (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.
A. Passeri (Tue,) studied this question.