Observation of $K_S^0$ semileptonic decays with CMD-2 detector

TL;DR

This paper reports the first observation of the semileptonic decay of the $K_S^0$ meson using the CMD-2 detector, measuring its branching ratio and confirming theoretical expectations.

Contribution

First experimental observation of $K_S^0 o \pi e u$ decay with a measured branching ratio consistent with theoretical predictions.

Findings

Observed 75 ± 13 events of the decay

Measured branching ratio is (7.2 ± 1.4)×10^{-4}

Results agree with theoretical calculations based on $K_L^0$ data

Abstract

The decay $K_S^0 \to \pi e \nu$ has been observed by the CMD-2 detector at the e^+e^- collider VEPP-2M at Novosibirsk. Of 6 million produced $K_L^0K_S^0$ pairs, $75 \pm 13$ events of the $K_S^0 \to \pi e \nu$ decay were selected. The corresponding branching ratio is $B(K_S^0 \to \pi e \nu)=(7.2 \pm 1.4)\times10^{-4}$. This result is consistent with the evaluation of $B(K_S^0 \to \pi e \nu)$ from the $K_L^0$ semileptonic rate and $K_S^0$ lifetime assuming $\Delta S=\Delta Q$ .