In the last few years it has become possible to study low energy pi pi
scattering in kaon decays to three pions, thanks to the high statistics
measurement of K+- -> pi+- pi0 pi0 decays performed by the NA48/2 experiment at
the CERN SPS. At the pi+ pi- threshold, the pi0 pi0 mass spectrum exhibits a
Wigner-cusp, from which the S-wave pi pi scattering lengths are extracted with
high precision. This measurement is complementary to the extraction of the
scattering lengths from K_e4 decays, which is also performed by the NA48/2
experiment.Comment: 10 pages, proceedings of plenary talk at MENU 2007, FZ Juelich, Sep
2007 (final version after referee's comments