Improved measurement of CP observables in B- --> D0CP K- decays

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We present a study of the decay B- -> D0CP K- and its charge conjugate, where D0CP 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 Y(4S) -> BBbar decays collected with the BABAR detector at the PEP-II e+e- storage ring. We measure the direct CP asymmetries ACP± and the ratios of the branching fractions RCP±: ACP+ = 0.27± 0.09(stat)± 0.04(syst), ACP- =-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 r²: x+ = -0.09± 0.05(stat)± 0.02(syst), x- = 0.10± 0.05(stat)± 0.03(syst), r² = 0.05± 0.07(stat)± 0.03(syst). These results will help to better constrain the phase parameter γ=(-VudVub*/VcdVcb*) of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.