Measurements of the Branching Fractions and Decay Distributions for KL->\pi\mu\nu\gamma and KL->\pi e\nu\gamma

TL;DR

This paper reports precise measurements of the branching fractions and decay distributions for KL decays involving a pion, lepton, neutrino, and photon, based on data from the 1997 KTeV experiment at Fermilab.

Contribution

It provides the first detailed measurements of R_Kl3rad ratios and decay distributions for KL->πμνγ and KL->πeνγ decays, including photon energy and angular distributions.

Findings

Measured R_Km3rad = (0.530 ± 0.019)%

Measured R_Ke3rad = (4.942 ± 0.062)%

Analyzed photon energy and lepton-photon angular distributions

Abstract

We present measurements of R_Kl3rad = Gamma(KL->\pi\ell\nu\gamma; Egcm > 10 MeV)/Gamma(KL->\pi\ell\nu), where ell = mu or e, and Egcm is the photon energy in the kaon rest frame. These measurements are based on KL decays collected in 1997 by the KTeV (E832) experiment at Fermilab. With samples of 1385 KL->\pi\mu\nu\gamma and 14221 KL->\pi\e\nu\gamma candidates, we find R_Km3rad = (0.530 +- 0.019)% and R_Ke3rad = (4.942 +- 0.062)%. We also examine distributions of photon energy and lepton-photon angle.