Observation of CP Violation in K(L)->pi+pi-e+e- Decays

TL;DR

This paper reports the first observation of a significant CP violation effect in K(L) decays to pi+pi-e+e-, demonstrating a large asymmetry in decay plane angles, marking a major discovery in particle physics.

Contribution

The study provides the first measurement of CP violation in K(L)->pi+pi-e+e- decays, revealing a large asymmetry in decay plane angles, and is the first to observe such an effect in an angular variable.

Findings

Observed a 13.6% asymmetry in decay distributions

First evidence of CP violation in this decay mode

Largest CP-violating effect observed in a decay mode

Abstract

We report the first observation of a manifestly CP violating effect in the K(L)->pi+pi-e+e- decay mode. A large asymmetry was observed in the distribution of these decays in the CP-odd and T-odd angle phi between the decay planes of the e+e- and pi+pi- pairs in the K(L) 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 integrating over the entire phase space of a mode and the first such effect observed in an angular variable.