First evidence for direct CP violation

Abstract

The double ratio R of the relative decay rates of the short- and long-lived neutral kaons into two charged and two neutral pions was measured to be 0.980±0.004±0.005. The deviation of R from the CP violation in the transition of the CP-odd K2 into two pions with ϵ′/ϵ=(3.3 ± 1.1)×10−3.