Observation of CP violation in the B^0 meson system

TL;DR

This paper reports an updated measurement of CP violation in the B^0 meson system using data from the BABAR detector, confirming CP violation with a significant asymmetry measurement consistent with the Standard Model.

Contribution

It provides the first measurement of sin2beta with increased data, establishing CP violation in B^0 mesons and refining previous results.

Findings

Measured sin2beta = 0.59 +/- 0.14 (stat) +/- 0.05 (syst)

Confirmed CP violation in B^0 mesons

Results are consistent with Standard Model predictions

Abstract

We present an updated measurement of time-dependent CP-violating asymmetries in neutral B decays with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. This result uses an additional sample of Upsilon(4S) decays collected in 2001, bringing the data available to 32 million B-anti-B pairs. We select events in which one neutral B meson is fully reconstructed in a final state containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the Standard Model is proportional to sin2beta, is derived from the decay time distributions in such events. The result sin2beta = 0.59 +/- 0.14 (stat) +/- 0.05 (syst) establishes CP violation in the B^0 meson system. We also determine |lambda| = 0.93 +/- 0.09 {stat} +/- 0.03 {syst}, consistent with no direct CP violation.