Measurement of CP Asymmetries and Branching Fractions in Charmless Two-Body B-Meson Decays to Pions and Kaons

TLDR: In this paper, improved measurements of CP-violation parameters in the decays B^0→π+π^+π-, B^ 0→K+π+, B^ 1.6±0.4×10^(-6), where in each case, the first uncertainties are statistical and the second are systematic, were obtained with the full data set collected at the Υ(4S) resonance by the BABAR experiment at the PEP-II asymmetric-energy B factory at the SLAC National Accelerator Laboratory.

Abstract: We present improved measurements of CP-violation parameters in the decays B^0→π^+π^-, B^0→K^+π^-, and B^0→π^0π^0, and of the branching fractions for B^0→π^0π^0 and B^0→K^0π^0. The results are obtained with the full data set collected at the Υ(4S) resonance by the BABAR experiment at the PEP-II asymmetric-energy B factory at the SLAC National Accelerator Laboratory, corresponding to (467±5)×10^6 BB pairs. We find the CP-violation parameter values and branching fractions: S_(π^+π^-)=-0.68±0.10±0.03, C_(π^+π^-)=-0.25±0.08±0.02, A_(K^-π^+)=-0.107±0.016_(-0.004)^(+0.006), C_(π^0π^0)=-0.43±0.26±0.05, B(B^0→π^0π^0)=(1.83±0.21±0.13)×10^(-6),  B(B^0→K^0π^0)= (10.1±0.6±0.4)×10^(-6), where in each case, the first uncertainties are statistical and the second are systematic. We observe CP violation with a significance of 6.7 standard deviations for B^0→π^+π^- and 6.1 standard deviations for B^0→K^+π^-, including systematic uncertainties. Constraints on the unitarity triangle angle α are determined from the isospin relations among the B→ππ rates and asymmetries. Considering only the solution preferred by the Standard Model, we find α to be in the range [71°,109°] at the 68% confidence level.