Determination of the ππ scattering lenghts from K^± -->π^±π⁰π⁰ decays

The NA48/2 experiment at the CERN SPS has collected more than 100 million fully reconstructed K±-->π±π0π0 decays. The preliminary analysis of a third of the data shows a sudden change of slope of the π0π0 invariant mass distribution in the region around 2m, where m is the mass of the charged pion. This anomaly, which was never observed before, is interpreted as a cusp-like effect resulting mainly from the contribution of the K±-->π±π0π0 decay amplitude through π+π- -->π0π0 charge exchange. The study of this phenomenon is a new and potentially more accurate method to measure a0-a2, the difference of the I = 0 and I = 2 S-wave scattering lengths. The colloquium will consist of two parts: the experiment, given by Italo Mannelli, and the theory by Nicola Cabibbo. Organiser(s): Luis Alvarez-Gaume / PH-THNote: * Tea & coffee will be served at 16.00 hrs.</i