Observation of CP Violation in B0→K+π− and B0→π+π−

Abstract

We report observations of C P violation in the decays B 0 → K + π − and B 0 → π + π − in a sample of 383 × 10 6 Υ ( 4 S ) → B ¯¯¯ B events. We find 4372 ± 82 B 0 → K + π − decays and measure the direct C P -violating charge asymmetry A K π = − 0.107 ± 0.018 ( stat ) + 0.007 − 0.004 ( syst ) , which excludes the C P -conserving hypothesis with a significance of 5.5 standard deviations. In the same sample, we find 1139 ± 49 B 0 → π + π − decays and measure the C P -violating asymmetries S π π = − 0.60 ± 0.11 ( stat ) ± 0.03 ( syst ) and C π π = − 0.21 ± 0.09 ( stat ) ± 0.02 ( syst ) . C P conservation in B 0 → π + π − ( S π π = C π π = 0 ) is excluded at a confidence level 1 − C . L . = 8 × 10 − 8 , corresponding to 5.4 standard deviations.