Improved measurement of CP observables in B^{±}→D_{CP}^{0}K^{±} decays

We present a study of the decay B-->(D(CP)K-)-K-0 and its charge conjugate, where D-(CP)(0) is reconstructed in both a non-CP flavor eigenstate and in CP (CP-even and CP-odd) eigenstates, based on a sample of 382 million Upsilon(4S) -> B (B) over bar decays collected with the BABAR detector at the PEP-II e(+)e(-) storage ring. We measure the direct CP asymmetries A(CP +/-) and the ratios of the branching fractions R-CP +/-: A(CP+)=0.27 +/- 0.09(stat) +/- 0.04(syst), A(CP-)=-0.09 +/- 0.09(stat) +/- 0.02(syst), RCP+=1.06 +/- 0.10(stat) +/- 0.05(syst), RCP-=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 gamma=arg(-VudVub*/VcdVcb*) of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.