Search for b→u transitions in B-→D0K- and B-→D*0K-

We search for B-→D0K- and B-→D*0K- and charge conjugates. Here the symbol D0 indicates decay of a D0 or D̄0 into K+π-, while the symbol D*0 indicates decay of a D*0 or D̄*0 to D0π0 or D0γ. These final states can be reached through the b→c transition B-→D(*)0K- followed by the doubly Cabibbo-Kobayashi-Maskawa (CKM)-suppressed D0→K+π-, or the b→u transition B-→D̄(*)0K- followed by the CKM-favored D̄0→K+π-. The interference of these two amplitudes is sensitive to the angle γ of the unitarity triangle. Our results are based on 232×106 Υ(4S)→BB̄ decays collected with the BABAR detector at SLAC. We find no significant evidence for these decays. We set a limit rB|A(B-→D̄0K-)/A(B-→D0K-)|<0.23 at 90% C.L. using the most conservative assumptions on the values of the CKM angle γ and the strong phases in the B and D decay amplitudes. In the case of the D* we set a 90% C.L. limit rB*2|A(B-→D̄*0K-)/A(B-→D*0K-) |2<(0.16)2 which is independent of assumptions on γ and strong phases.