Observation of the rare decay Ks->pi0e+e-

TL;DR

This paper reports the first observation and measurement of the rare decay Ks->pi0e+e- at CERN, providing a new precise estimate of its branching fraction based on experimental data.

Contribution

The study presents the first measurement of the branching fraction for Ks->pi0e+e-, using data from the NA48/1 experiment, with detailed background estimation and analysis.

Findings

Measured BR(Ks->pi0e+e-) = (5.8^{+2.9}_{-2.4}) x 10^{-9}

Observed 7 events with a background of 0.15 events

Provides the first experimental evidence for this rare decay

Abstract

A search for the decay Ks->pi0e+e- has been made by the NA48/1 experiment at the CERN SPS accelerator. Using data collected during 89 days in 2002 with a high-intensity Ks beam, 7 events were found with a background of 0.15 events. The branching fraction BR(Ks->pi0e+e-, m(ee) > 0.165 GeV/c^2) = (3.0^{+1.5}_{-1.2}(stat) +/-0.2 (syst)) x 10^{-9} has been measured. Using a vector matrix element and a form factor equal to one, the measurement gives BR(Ks->pi0e+e-) = (5.8^{+2.9}_{-2.4}) x 10^{-9}.