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.
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The KLOE-2 collaboration., Babusci, D., Berlowski, M. et al. Measurement of the KS → πeν branching fraction with the KLOE experiment. J. High Energ. Phys. 2023, 98 (2023). https://doi.org/10.1007/JHEP02(2023)098
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DOI: https://doi.org/10.1007/JHEP02(2023)098