Observation of CP violation in the $B^0$ system

TL;DR

This paper reports the first observation of CP violation in the $B^0$ meson system, using data from the BABAR detector, measuring a significant asymmetry that confirms CP violation at the 4-sigma level.

Contribution

The study provides the first measurement of CP violation in the $B^0$ system, establishing this phenomenon with statistical significance using time-dependent asymmetries.

Findings

Measured $ ext{sin}2eta=0.59 \, extpm \, 0.14 ext{(stat)} \, extpm \, 0.05 ext{(syst)}$

Established CP violation in the $B^0$ system at 4$\sigma$ significance

Performed $B$ lifetime and mixing measurements from 23 million $Bar B$ pairs

Abstract

The BABAR detector, operating at energies near the $\Upsilon(4S)$ resonance at the PEP-II asymmetric $B$ Factory at SLAC, has collected a sample of 32 million $B\bar B$ pairs by May 2001. A study of time-dependent CP-violating asymmetries in events where one neutral $B$ meson is fully reconstructed in a final state containing charmonium has resulted in the measurement $\sin2\beta=0.59 \pm 0.14 {\rm (stat)} \pm 0.05 {\rm (syst)}$, which establishes CP violation in the $B^0$ meson system at the 4$\sigma$ level. $B$ lifetime and mixing measurements from a sub-sample of 23 million $B\bar B$ pairs are also presented.