Observation of CP Violation in B0 -> K+pi- and B0 -> pi+pi-

TL;DR

This paper reports the observation of CP violation in B0 meson decays to K+pi- and pi+pi-, providing significant evidence against CP conservation in these processes.

Contribution

It presents the first significant measurements of direct CP violation in B0 -> K+pi- and B0 -> pi+pi- decays with high statistical significance.

Findings

CP violation observed in B0 -> K+pi- with 5.5 sigma significance

CP violation observed in B0 -> pi+pi- with 5.4 sigma significance

Measured asymmetries are Akpi = -0.107 and Spipi = -0.60

Abstract

We report observations of CP violation in the decays B0 -> K+pi- and B0 -> pi+pi- in a sample of 383 million Y(4S) -> BBbar events. We find 4372 +/- 82 B0 -> K+pi- decays and measure the direct CP-violating charge asymmetry Akpi = -0.107 +/- 0.018 (stat) +0.007-0.004 (syst), which excludes the CP-conserving hypothesis with a significance of 5.5 standard deviations. In the same sample we find 1139 +/- 49 B0 -> pi+pi- decays and measure the CP-violating asymmetries Spipi = -0.60 +/- 0.11 (stat) +/- 0.03 (syst) and Cpipi = -0.21 +/- 0.09 (stat) +/- 0.02 (syst). CP conservation in B0 -> pi+pi- (Spipi=Cpipi=0) is excluded at a confidence level 1-C.L. = 8 * 10^{-8}, corresponding to 5.4 standard deviations.