Improved Measurements of CP-Violating Asymmetry Amplitudes in B0→π+π− Decays

Abstract

We present updated measurements of the C P -violating parameters S π π and C π π in B 0 → π + π − decays. Using a sample of 227 × 10 6 Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at the PEP-II asymmetric-energy e + e − collider at SLAC, we observe 467 ± 33 signal decays and measure S π π = − 0.30 ± 0.17 ( stat ) ± 0.03 ( syst ) and C π π = − 0.09 ± 0.15 ( stat ) ± 0.04 ( syst ) .