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

We search for B-→D˜0K- and B-→D˜*0K- and charge conjugates. Here the symbol D˜0 indicates decay of a D0 or D̅ 0 into K+π-, while the symbol D˜*0 indicates decay of a D*0 or D̅ *0 to D˜0π0 or D˜0γ. 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-→D̅ (*)0K- followed by the CKM-favored D̅ 0→K+π-. The interference of these two amplitudes is sensitive to the angle γ of the unitarity triangle. Our results are based on 232×10^6 Υ(4S)→BB̅ decays collected with the BABAR detector at SLAC. We find no significant evidence for these decays. We set a limit rB≡|A(B-→D̅ 0K-)/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-→D̅ *0K-)/A(B-→D*0K-)|2<(0.16)2 which is independent of assumptions on γ and strong phases.