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Very large samples of charged kaon decays have been accumulated in 2003-2004 by the NA48/2 experiment at the CERN SPS. Among many rare decay modes, the analysis of K± → π+π−e±ν (Ke4) decays allows a quasi model-independent approach to the study of low energy ππ scattering. From a data sample of more than 1 million Ke4 decays, the form factors and their energy dependence are simultaneously measured with an improved precision. From the evolution of the ππ phsase shift close to threshold, scattering lengths can be extracted with an experimental precision of few percents, providing an accurate test of Chiral Perturbation Theory predictions. This result can be combined with the independent but complementary NA48/2 result obtained in the analysis of 60 millions K± → π0π0π± (K3π ), leading to an experimental measurement of a0 and a2, the isospin 0 and 2 S-wave ππ scattering lengths, of unprecedented precision.

Precise tests of chiral perturbation theory from Ke4 decays by the NA48/2 experiment