Measurement of the branching fraction and decay rate asymmetry of B-→Dπ+π-π0K-

We report the observation of the decay B-→Dπ+π-π0K-, where Dπ+π-π0 indicates a neutral D meson detected in the final state π+π-π0, excluding KS0π0. This doubly Cabibbo-suppressed decay chain can be used to measure the CKM phase γ. Using about 229×106 e+e-→BB̅ events recorded by the BABAR experiment at the PEP-II e+e- storage ring, we measure the branching fraction B(B-→Dπ+π-π0K-)=(5.5±1.0(stat.)±0.7(syst.))×10-6 and the decay rate asymmetry A(B-→Dπ+π-π0K-)=-0.02±0.16(stat.)±0.03(syst.) for the full decay chain.