Improved measurement of CP observables in B±→D0CPK± decays

Abstract

We present a study of the decay B − → D 0 ( C P ) K − and its charge conjugate, where D 0 ( C P ) is reconstructed in both a non- C P flavor eigenstate and in C P ( C P -even and C P -odd) eigenstates, based on a sample of 382 million Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at the PEP-II e + e − storage ring. We measure the direct C P asymmetries A C P ± and the ratios of the branching fractions R C P ± : A C P + = 0.27 ± 0.09 ( stat ) ± 0.04 ( syst ) , A C P − = − 0.09 ± 0.09 ( stat ) ± 0.02 ( syst ) , R C P + = 1.06 ± 0.10 ( stat ) ± 0.05 ( syst ) , R C P − = 1.03 ± 0.10 ( stat ) ± 0.05 ( syst ) . We also express the results in terms of the so-called Cartesian coordinates x + , x − , and r 2 : x + = − 0.09 ± 0.05 ( stat ) ± 0.02 ( syst ) , x − = 0.10 ± 0.05 ( stat ) ± 0.03 ( syst ) , r 2 = 0.05 ± 0.07 ( stat ) ± 0.03 ( syst ) . These results will help to better constrain the phase parameter γ = arg  ( − V u d V ∗ u b / V c d V ∗ c b ) of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.