Studies of the Decay B±→DCPK±

We report studies of the Cabibbo-suppressed decay B+/- --> DCPK+/-, where D-CP denotes CP eigenstates of the D-0 - (D) over bar (0) system. The analysis is based on a 29.1 fb(-1) sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric e(+)e(-) storage ring. We measure ratios of branching fractions, relative to Cabibbo-favored B+/--->D(CP)pi+/-, of B>(B- --> D1K-)/B(B- --> D(1)pi(-)) = 0.125 +/-0.036 +/- 0.010 and B(B- --> D2K-)/B(B- --> D(2)pi(-)) = 0.119 +/- 0.028 +/- 0.006; the index 1 (2) denotes the CP = +1 (-1) eigenstate. We also extract the partial rate asymmetries for B+/- --> DCPK+/-, finding A(1) = 0.29 +/- 0.26 +/- 0.05 and A(2) = -0.22 +/- 0.24 +/- 0.04.