First observation of the KS->pi0 gamma gamma decay

TL;DR

This paper reports the first observation of the rare decay KS->pi0 gamma gamma, measuring its branching ratio and confirming theoretical predictions.

Contribution

It provides the first experimental measurement of the KS->pi0 gamma gamma decay, validating Chiral Perturbation Theory predictions.

Findings

Observed 31 decay candidates with background estimate of 13.7 events.

Measured branching ratio of (4.9 +- 1.6(stat) +- 0.9(syst)) x 10^-8.

Results agree with theoretical predictions.

Abstract

Using the NA48 detector at the CERN SPS, 31 KS->pi0 gamma gamma candidates with an estimated background of 13.7 +- 3.2 events have been observed. This first observation leads to a branching ratio of BR(KS->pi0 gamma gamma) = (4.9 +- 1.6(stat) +- 0.9(syst)) x 10^-8 in agreement with Chiral Perturbation theory predictions.