Determination of the $a_{0}-a_{2}$ pion scattering length from $K^{+} \to \pi^{+}\pi^{0}\pi^{0}$ decay

We present a new method for the determination of the pion-pion scattering lenght combination a0-a2, based on the study of the pi0-pi0 spectrum in K->pi+ pi0 pi0 in the vicinity of the pi+ pi- threshold. The method requires a minimum of theoretical input, and is potentially very accurate.