First Observation of the Decays (B)over-bar(0) -> D+K-pi(+)pi(-) and B- -> (DK-)-K-0 pi(+)pi(-)

First observations of the Cabibbo-suppressed decays B¯0 → D+K-π+π- and B- → D0K-π+π- are reported using 35 pB-1 of data collected with the LHCb detector. Their branching fractions are measured with respect to the corresponding Cabibbo-favored decays, from which we obtain B(B¯0→ D+K-π+π-)/B(B¯0→D+π-π+π-)=(5.9±1.1±0.5)×10-2 and B(B-→D0K-π+π-)/B(B-→ D0π-π+π-)=(9.4±1.3±0.9)×10-2, where the uncertainties are statistical and systematic, respectively. The B- → D0K-π+π- decay is particularly interesting, as it can be used in a similar way to B- → D0K- to measure the Cabibbo-Kobayashi-Maskawa phase γ. © 2012 CERN