Detailed study of $K_{e4}$ decay properties by the NA48/2 experiment at CERN

A sample of 1.13 million Ke4+−(K±→π+π−e±ν) decays and 65210Ke400(K±→π0π0e±ν) decays has been collected in 2003–2004 by the NA48/2 collaboration at the CERN SPS. Branching ratio and form factors in the S- and P-wave have been measured at a percent level precision. The comparison of Branching ratio and form factor values in both modes sheds new light on isospin symmetry breaking effects. Form factor measurements are major inputs to the study of low energy QCD and bring stringent tests of Chiral Perturbation Theory predictions.