Measurement of CP observables in B+- --> DCP K+- decays and constraints on the CKM angle gamma
Abstract
Using the entire sample of 467 million Y(4S) --> BBbar decays collected with the BaBar detector at the PEP-II asymmetric-energy B factory at SLAC, we perform a "GLW" analysis of B+- --> D K+- decays, using decay modes in which the neutral D meson decays to either CP-eigenstates or non-CP-eigenstates. We measure the partial decay rate charge asymmetries for CP-even and CP-odd D final states to be ACP+ = 0.25+-0.06+-0.02 and ACP- = -0.09+-0.07+-0.02, respectively, where the first error is the statistical and the second is the systematic uncertainty. The parameter ACP+ is different from zero with a significance of 3.6 standard deviations, constituting evidence for direct CP violation. We also measure the ratios of the charged-averaged B partial decay rates in CP and non-CP decays, RCP+ = 1.18+-0.09+-0.05 and RCP- = 1.07+-0.08+-0.04. We infer frequentist confidence intervals for the angle gamma of the (db) unitarity triangle, for the strong phase difference deltaB, and for the amplitude ratio rB, which are related to the B- --> DK- decay amplitude by rBei(deltaB-gamma) = A(B- --> anti-D0 K-)/A(B- --> D0 K-). Including statistical and systematic uncertainties, we obtain 0.24<rB<0.45 (0.06<rB<0.51) and, modulo 180 degrees, 11.3 degrees < gamma < 22.7 degrees or 80.9 degrees < gamma < 99.1 degrees or 157.3 degrees < gamma < 168.7 degrees (7.0 degrees < gamma < 173.0 degrees) at the 68% (95%) confidence level.