Measurement of the cp-violation parameter η+-γ in neutral kaon decays

Interference between KS and KL decays into the final state π+π-γ has been observed in experiment 731 at Fermilab. By fitting the distribution of decays downstream of a regenerator, a new CP-violation parameterη+-γ, analogous to η+-, has been measured, with its magnitude equal to(2.15±0.26±0.20)×10-3, and φ+-γ, the associated phase angle, equal to(72±23±17)°. Assuming that any difference between this fit value for η+-γ and the previously measured value forη+- can be attributed to direct CP violation in this decay, a limit of|ε+-γ′|/ε<0.3 at the 90% confidence level has been made.