Radiative K+- Decays from NA48/2

TL;DR

This paper reports new measurements of radiative K+- decays from the NA48/2 experiment, including the first interference measurement, precise branching fractions, and the first observation of the K+- -> pi+- e+ e- gamma decay, advancing understanding of kaon decay processes.

Contribution

It provides the first measurement of interference effects in K+- -> pi+- pi0 gamma decays and the first observation of the K+- -> pi+- e+ e- gamma decay, with precise branching fractions.

Findings

First measurement of interference between direct photon emission and inner bremsstrahlung.

Precise branching fraction for K+- -> pi+- gamma gamma.

First observation of K+- -> pi+- e+ e- gamma decay.

Abstract

New results on radiative K+- decays from the NA48/2 experiment are presented. In the channel K+- -> pi+- pi0 gamma more than 1 million decays were reconstructed, leading to the first measurement of the interference between direct photon emission and inner bremsstrahlung and stringent limits on CP violation in this decay. For K+- -> pi+- gamma gamma, a precise measurement of the branching fraction was performed, based on more than 1000 events. In addition, the related decay K+- -> pi+- e+ e- gamma was observed for the first time and measurements of the decay rate and the decay parameter c^ were carried out.