Narrow Results

Large samples of K^± → 3π and K^± → π⁺π^-e^±ν (K_e4) decays have been collected by the NA48/2 experiment at CERN SPS.

At the π⁺π^- threshold, the π⁰π⁰ invariant mass spectrum of the decay K^± → π^±π⁰π⁰ xhibits a Wigner cusp, from which the S-wave ππ scattering lengths are extracted with high precision.

The same scattering lengths are also independently determined from the accurate measurement of the form factors in the K_e4 decay K^± → π⁺π^-e^±ν.