Search for the K(S) --> e+e- decay with the KLOE detector at DAFNE

TL;DR

This paper reports a search for the rare decay KS --> e+e- using the KLOE detector at DAFNE, setting a new upper limit that surpasses previous results by a factor of seven, with implications for testing the Standard Model.

Contribution

First direct search for KS --> e+e- decay at DAFNE, providing a significantly improved upper limit on its branching ratio.

Findings

BR(KS --> e+e-) < 2.1×10^-8 at 90% CL

Improved sensitivity by a factor of ~7 over previous experiments

Utilized optimized background rejection techniques.

Abstract

We present results of a direct search for the decay KS --> e+e- with the KLOE detector, obtained with a sample of e+e- --> phi --> KSKL events produced at DAFNE, the Frascati phi-factory, for an integrated luminosity of 1.3fb-1. The Standard Model prediction for this decay is BR(KS --> e+e-) = 1.6*10^-15. The search has been performed tagging the KS decays by simultaneous detection of a KL interaction in the calorimeter. Background rejection has been optimized by using both kinematic cuts and particle identification. At the end of the analysis chain we find BR(KS --> e+e-) < 2.1*10^-8 at 90% CL, which improves by a factor of ~7 on the previous best result, obtained by CPLEAR experiment.