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

Abstract

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 $\varphi \to K_L{K}_S$ 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 $\mathcal{B}(K_S\to \pi e\nu )=(7.211\pm 0.046_{\mathrm{stat}}\pm 0.052_{\mathrm{syst}})\times 10^{-4}$. The combination with our previous measurement gives $\mathcal{B}(K_S\to \pi e\nu )=(7.153\pm 0.037_{\mathrm{stat}}\pm 0.043_{\mathrm{syst}})\times 10^{-4}$. From this value we derive $f_{+}(0)|V_{us}|=0.2170\pm 0.009$.

arXiv admin note: substantial text overlap with arXiv:1912.05990