Study of the Decays KL -> pi+ pi- gamma and KL -> pi+ pi- e+ e- at KTeV

TL;DR

This paper reports new measurements of rare KL decay modes, including the first direct form factor measurement for KL -> pi+ pi- gamma, and explores T-violation in KL -> pi+ pi- e+ e- decays, providing insights into chiral models and decay dynamics.

Contribution

It presents the first direct measurement of the form factor for KL -> pi+ pi- gamma decays and investigates T-violation in KL -> pi+ pi- e+ e- decays.

Findings

First direct measurement of the form factor for KL -> pi+ pi- gamma.

Evidence of T-violating asymmetry in KL -> pi+ pi- e+ e- angular distribution.

Form factor and branching ratios relevant for decay modeling.

Abstract

We present new results on the related rare KL decay modes KL -> pi+ pi- gamma and KL -> pi+ pi- e+ e-. KTeV has performed the first direct measurement of the form factor for the "direct emission" component of KL -> pi+ pi- gamma decays, a quantity with ramifications for particular chiral models. In addition, the form factor and direct emission/inner bremsstrahlung branching ratio - also presented here - are important input parameters for the understanding of the planar-angle distribution of KL -> pi+ pi- e+ e- decays. Preliminary results indicating the presence of a T-violating asymmetry in the KL -> pi+ pi- e+ e- angular distribution are presented.