Pion scattering lengths from NA48

The anomaly (cusp) in the mass spectrum of 2 π 0 from K ± → π ± π 0 π 0 decay has been observed in the NA48/2 experiment. Using the recently developed interpretation of this effect in terms of Chiral Perturbative Theory, the pion scattering parameters are measured. The preliminary result for the pion scattering length difference, based on the part of statistics, is ( a 0 − a 2 ) m π + = 0.281 ± 0.007 ( stat ) ± 0.014 ( syst ) ± 0.014 ( extern ) .