Measurements of Ke4 and K+- -> pi0 pi0 pi+- decays

TL;DR

This paper reports precise measurements of Ke4 and K+- -> pi0 pi0 pi+- decays, extracting pi-pi scattering lengths and testing Chiral Perturbation Theory with large data samples.

Contribution

It provides new, precise measurements of decay form factors, branching fractions, and pi-pi scattering lengths, advancing the understanding of low-energy QCD.

Findings

Measured pi-pi scattering lengths a00 and a20.

Determined branching fraction and form factors of Ke400 decay.

Validated Chiral Perturbation Theory predictions.

Abstract

The NA48/2 experiment at the CERN SPS collected in 2003 and 2004 large samples of the decays K+- -> pi+ pi- e+- nu (Ke4+-), K+- -> pi0 pi0 e+- nu (Ke400) and K+- -> pi0 pi0 pi+-. From the Ke4+- form factors and from the cusp in the M00^2 distribution of the K+- -> pi0 pi0 pi+- events, the pi-pi scattering lengths a00 and a20 could be extracted. This measurement is a fundamental test of Chiral Perturbation Theory (ChPT). The branching fraction and form factors of the Ke400 decay were precisely measured, using a much larger data sample than in previous experiments.