Study of $K^+ \rightarrow \pi^{0} e^{+} \nu \gamma $ decay with OKA setup

TL;DR

This paper reports on the measurement of the rare decay $K^+ ightarrow \pi^{0} e^{+} u \gamma$ at the OKA experiment, including differential spectra and branching ratios, confirming theoretical predictions.

Contribution

First measurement of the $K^+ ightarrow \pi^{0} e^{+} u \\gamma$ decay with detailed spectra and branching ratios, supporting ChPT $O(p^{4})$ calculations.

Findings

Observed over 32,000 decay events.

Measured branching ratio for specific photon energy and angle cuts.

Results agree with ChPT $O(p^{4})$ theoretical predictions.

Abstract

Results of a study of the $K^+ \rightarrow \pi^{0} e^{+} \nu \gamma $ decay at OKA setup are presented. More than 32000 events of this decay are observed. The differential spectra over the photon energy and the photon-electron opening angle in kaon rest frame are presented. The branching ratios, normalized to that of $K_{e3}$ decay are calculated for different cuts in $E^*_\gamma$ and $cos\Theta^{*}_{e\gamma}$. In particular, the branching ratio for $E^{*}_{\gamma}>30$ MeV and $\Theta^{*}_{e \gamma}>20^{\circ}$ is measured R = $\frac{Br(K^+ \rightarrow \pi^{0} e^{+} \nu_{e} \gamma) } {Br(K^+ \rightarrow \pi^{0} e^{+} \nu_{e})} $ = =(0.587$\pm$0.010($stat.$)$\pm$0.015($syst.$))$\times10^{-2}$, which is in a good agreement with ChPT $O(p^{4})$ calculations.