Measurement of the branching fraction for the decay $K_S \to \pi \mu \nu$ with the KLOE detector

TL;DR

This paper reports a precise measurement of the branching fraction for the rare decay $K_S o \pi \mu u$ using the KLOE detector, employing advanced selection techniques and normalization to known decay modes.

Contribution

The study provides the first detailed measurement of the $K_S o \pi \mu u$ branching fraction with improved accuracy using a large data sample and sophisticated analysis methods.

Findings

Branching fraction measured as (4.56 ± 0.11_stat ± 0.17_syst)×10^{-4}

Identified 7223 ± 180 signal events

Used boosted decision trees and time-of-flight for decay selection

Abstract

Based on 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 we have measured the branching fraction for the decay $K_S \to \pi \mu \nu$. The $K_S$ mesons are identified by the interaction of $K_L$ mesons in the detector. The $K_S \to \pi \mu \nu$ decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of $K_L \to \pi \mu \nu$ decays. A fit to the reconstructed muon mass distribution finds $7223 \pm 180$ signal events. Normalising to the $K_S \to \pi^+ \pi^-$ decay events the result for the branching fraction is $\mathcal{B}(K_S \to \pi \mu \nu) = (4.56 \pm 0.11_{\rm stat} \pm 0.17_{\rm syst})\times10^{-4}$.