We report the first observation of a manifestly CP violating effect in the KL → π+π−e+e− decay mode. A large asymmetry was observed in the distribution of these decays in the CP-odd and T-odd angle φ between the decay planes of the e+e− and π+π− pairs in the KL center of mass system. After acceptance corrections, the overall asymmetry is found to be [13.6 ± 2.5(stat) ± 1.2(syst)]%. This is the largest CP-violating effect yet observed when integrating over the entire phase space of a mode and the first such effect observed in an angular variable.
ASJC Scopus subject areas
- Physics and Astronomy(all)