Cusps in K --> 3pi decays: a theoretical framework

Understand

Based on the analysis of 6.031*10^7 K+- --> pi0 pi0 pi+- decays, the NA48/2 collaboration has recently determined the S-wave pi-pi scattering lengths a_0-a_2 with high precision.

• In addition, the scattering length a_2 has been independently measured, although less precisely so.
• The present article discusses in detail one of the theoretical frameworks used in the data analysis.