Precision measurement of kaon radiative decays at NA48

Abstract

The kaon decays are an excellent laboratory to test low energy strong interaction perturbative theories. Recent results on radiative K ± decays from CERN NA48/2 experiment are presented. In the channel K ± → π ± π 0 γ more than a million reconstructed decays have lead to the precision measurement of both the direct photon emission and inner bremsstrahlung amplitudes, with their interference term being observed for the first time. In addition the CP violating asymmetry between K + and K - has been obtained to be less than 10 − 3 in this channel. We also report on the measurement of the branching fraction of the rare decay K ± → π ± γ γ using more than 1000 events from 20% of the full NA48/2 data set. From the spectrum of γγ mass the decay parameter ĉ has been extracted with unprecedented precision. We measure in a model independent way the decay rate of the process K ± → π ± e + e − γ , never observed before, using 120 events.