Two measurements of ππ scattering lengths [formula omitted] and [formula omitted] from studies of [formula omitted] decays with the CERN-NA48/2 experiment

Abstract

The NA48 experiment at the CERN SPS has used K L 0 and K S 0 kaons for the precise measurement of the direct CP violation parameter Re ( ɛ ′ / ɛ ) . In 2002 it was re-designed as NA48/2 to search for CP violation in K ± → 3 π decays. This configuration has also allowed studying several rare decay processes of charged kaons to test chiral perturbation theory. With data samples of ∼ 10 6 K ± → π ± π − e ± ν decays, precise values of a 0 and a 2 , the isospin I=0 and I=2 s -wave ππ scattering lengths, are extracted with an unprecedented experimental precision. The same scattering lengths are also measured using ∼ 60 × 10 6 K ± → π ± π 0 π 0 decays where a cusp structure in the Dalitz plot has been observed for the first time.