Observation of the radiative kaon decay K- --> mu-pi0gammanu

TL;DR

This paper reports the first observation of the radiative decay of a kaon into a muon, pion, photon, and neutrino, with measurements aligning with some theoretical predictions but showing discrepancies in angular asymmetry.

Contribution

It presents the first experimental observation of the K- --> mu- pi0 gamma nu decay and compares measured branching ratios and asymmetries with theoretical models.

Findings

Branching ratio ratios consistent with theory in certain energy regions

Angular distribution asymmetry measured with notable deviation from prediction

T-odd asymmetry measured near zero, indicating no significant CP violation evidence

Abstract

Using data collected with the ISTRA+ spectrometer during the 2001 run of the U-70 proton synchrotron in Protvino, we report the first observation of the radiative kaon decay K- -->mu-pi0gammanu. We find Br(Kmu3g)/Br(Kmu3) for two regions 5<Eg<30 and 30<Eg<60 MeV consistent with theoretical predictions. The measured angular distribution asymmetry for the first region, 0.093+/-0.141, is two standard deviations away from the theoretical prediction of 0.354. The measured asymmetry in the T-odd variable is -0.03+/-0.13.