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

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.