New measurement of the amplitude of the CP conserving decay KS0 → π+π−π0

We measured the amplitude for the CP-symmetry-conserving decay KS0 → π+π−π0 in an experiment at Fermilab. This decay manifests itself as a time dependent charge asymmetry in the interference between the coherent KS and KL decays. We collected 1.1 million π+π−π0 decays between 0.6 and 7.6 KS lifetimes from the production target using a detector that consisted of a magnetic spectrometer and a lead glass electromagnetic calorimeter. The ratio ϱ+−0 of the CP-conserving KS amplitude to the KL amplitude is found to be: ∥ϱ+−0∥=0.039−0.006+0.009(stat.)±0.005(syst.), with a phas φϱ = −9° ± 18°. This yields a branching ratio of (4.8−1.6+2.2(stat.)±1.1(syst.)) × 10−7.