New measurement of the charged kaon semileptonic (Ke4) decay Branching Ratio and Hadronic Form Factors

TL;DR

This paper reports a precise measurement of the branching ratio and hadronic form factors in charged kaon semileptonic (Ke4) decay, using a large data sample from the NA48/2 experiment at CERN, enhancing understanding of kaon decay dynamics.

Contribution

It provides the first absolute measurement of the hadronic form factors and the branching ratio for Ke4 decay with high precision, complementing previous scattering studies.

Findings

Branching ratio BR(Ke4) = (4.257 +/- 0.016_exp +/- 0.031_ext) x 10^-5

Form factor normalization f_s = 5.705 +/- 0.017_exp +/- 0.031_ext

Total relative errors below 1% for both measurements

Abstract

A sample of more than one million Ke4 decay candidates with less than one percent background contamination has been collected by the NA48/2 experiment at the CERN SPS in 2003-2004, allowing a detailed study of the decay properties. The branching ratio, inclusive of radiative Ke4gamma decays, is measured to be BR(Ke4) = (4.257 +/- 0.016_exp +/- 0.031_ext) x 10-5 with a total relative error of 0.8%. This measurement complements the study of S- and P-wave hadronic form factors by assigning absolute values to the relative hadronic form factors obtained earlier in a simultaneous analysis of the pion-pion scattering lengths conducted on the same data sample. The overall form factor normalization f_s = 5.705 +/- 0.017_exp +/- 0.031_ext is obtained with a total relative precision of 0.6%.