Measurement of the \(K_S \to \pi e \nu\) branching fraction with the KLOE experiment

• Published in: arXiv.org 2023-01
• Main Authors: Babusci, D, Berlowski, M, Bloise, C, Bossi, F, Branchini, P, Cao, B, Ceradini, F, Ciambrone, P, Curciarello, F, Czerwiński, E, D'Agostini, G, D'Amico, R, Danè, E, De Leo, V, De Lucia, E, De Santis, A, De Simone, P, A Di Cicco, A Di Domenico, Diociaiuti, E, Domenici, D, D'Uffizi, A, Fantini, G, Gajos, A, Gamrat, S, Gauzzi, P, Giovannella, S, Graziani, E, Kang, X, Kupsc, A, Mandaglio, G, Martini, M, Miscetti, S, Moskal, P, Passeri, A, Perez del Rio, E, Schioppa, M, Selce, A, Silarski, M, Sirghi, F, Solodov, E P, Wiślicki, W, Wolke, M
• Format: Article
• Language: English
• Subjects: Decay; Decision trees; Electron mass; Mass distribution; Mesons
• ISSN: 2331-8422

The branching fraction for the decay \(K_S \to \pi e \nu\) has been measured with a sample of 300 million \(K_S\) mesons produced in \(\phi \to K_L K_S\) decays recorded by the KLOE experiment at the DA\(\Phi\)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 \(K_L \to \pi e \nu\) 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 \(K_S \to \pi^+\pi^-\) decay events the result for the branching fraction is \(\mathcal{B}(K_S \to \pi e \nu) = (7.211 \pm 0.046_{\rm stat} \pm 0.052_{\rm syst}) \times10^{-4}\). The combination with our previous measurement gives \(\mathcal{B}(K_S \to \pi e \nu) = (7.153 \pm 0.037_{\rm stat} \pm 0.043_{\rm syst}) \times10^{-4}\). From this value we derive \(f_+(0)|V_{us}| = 0.2170 \pm 0.009\).