TESTS OF CHPT WITH ${\rm K}_{{\rm e}4}^{+-}$ AND ${\rm K}_{{\rm e}4}^{00}$ DECAYS AT THE NA48/2 EXPERIMENT AT CERN

Abstract

The NA48/2 experiment has collected the largest samples to date of semi-leptonic charged kaon decays in the [Formula: see text] (K± → π+π-e±ν) and [Formula: see text] (K± → π0π0e±ν) modes. From 1.1 million [Formula: see text] decays, form factors in the S- and P-wave have been extensively studied. Branching ratio and form factors have been measured at unprecedented precision. From ~ 66000 [Formula: see text] decays, preliminary values of the Branching ratio and form factor have been obtained at a percent level precision. The comparison of Branching ratio and form factor values in both Ke4 modes sheds new light on isospin symmetry breaking effects. Form factor measurements are major inputs to the study of low energy QCD and are powerful tests of Chiral Perturbation Theory predictions.