Measurement of the $K_S \to πe ν$ branching fraction with the KLOE experiment
hep-ex
/ Authors
D. Babusci, M. Berlowski, C. Bloise, F. Bossi, P. Branchini, B. Cao, F. Ceradini, P. Ciambrone, F. Curciarello, E. Czerwiński
and 33 more authors
G. D'Agostini, R. D'Amico, E. Danè, V. De Leo, E. De Lucia, A. De Santis, P. De Simone, A. Di Cicco, A. Di Domenico, E. Diociaiuti, D. Domenici, A. D'Uffizi, G. Fantini, A. Gajos, S. Gamrat, P. Gauzzi, S. Giovannella, E. Graziani, X. Kang, A. Kupsc, G. Mandaglio, M. Martini, S. Miscetti, P. Moskal
/ Abstract
The branching fraction for the decay $K_S \to πe ν$ has been measured with a sample of 300 million $K_S$ mesons produced in $φ\to K_L K_S$ decays recorded by the KLOE experiment at the DA$Φ$NE $e^+e^-$ collider. Signal decays are selected by a boosted decision tree built with kinematic variables and time-of-flight measurements. Data control samples of $K_L \to πe ν$ decays are used to evaluate signal selection efficiencies. A fit to the reconstructed electron mass distribution finds 49647$\pm$316 signal events. Normalising to the $K_S \to π^+π^-$ decay events the result for the branching fraction is $\mathcal{B}(K_S \to πe ν) = (7.211 \pm 0.046_{\rm stat} \pm 0.052_{\rm syst}) \times10^{-4}$. The combination with our previous measurement gives $\mathcal{B}(K_S \to πe ν) = (7.153 \pm 0.037_{\rm stat} \pm 0.043_{\rm syst}) \times10^{-4}$. From this value we derive $f_+(0)|V_{us}| = 0.2170 \pm 0.009$.