CP Violation Problem

TL;DR

This review discusses the history, experimental observations, and ongoing questions regarding CP violation in meson decays, highlighting its small magnitude and the challenges in understanding its origins within the Standard Model or beyond.

Contribution

It provides a comprehensive overview of experimental data on CP violation across various mesons and discusses open questions about its fundamental nature and magnitude.

Findings

Observation of indirect CP violation at ~10^{-3}

Discovery of direct CP violation at ~10^{-6}

CP violation in charged kaon decays confirmed

Abstract

The strong CP violation problem has a long history emanating from its discovery 60 years ago in the decay of neutral kaons and subsequent experimental and theoretical studies over several decades. We review herein experimental data that observe indirect CP violation of the order of $\sim10^{-3}$, as well as the discovery of direct CP violation of the order of $\sim10^{-6}$. Despite improved experimental methods over the past half a century, the original CP violation numbers have remained the same. Verification of the CP violation in the decay of charged kaons was also observed. Data reflecting CP violation in the decays of $B$ and $D$ mesons have become very important and are also discussed in this review. The question of CP violation only with the participation of $s\bar{s}$, $c\bar{c}$, and $b\bar{b}$ quarks in the framework of the Standard Model or beyond it and its small magnitude remains open.