Study of B− → D K− π+ π− and B− → D π− π+ π− Decays and Determination of the CKM Angle γ

We report a study of the suppressed B− → D K− π+ π− and favored B− → D π− π+ π− decays, where the neutral D meson is detected through its decays to the K∓ π± and CP-even K+ K− and π+ π− final states. The measurement is carried out using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 3.0 fb^−1. We observe the first significant signals in the CP-even final states of the D meson for both the suppressed B− → D K− π+ π− and favored B− → D π− π+ π− modes, as well as in the doubly Cabibbo suppressed D → K+ π− final state of the B− → D π− π+ π− decay. Evidence for the suppressed decay B− → D K− π+ π−, with D → K+ π−, is also presented. From the observed yields in the B− → D K− π+ π−, B− → D π− π+ π− and their charge conjugate decay modes, the most probable value of the weak phase γ corresponds to γ = (74{−19}{+20})°. This is one of the most precise single-measurement determinations of γ to date.