Study of $B^{-}\to DK^-π^+π^-$ and $B^-\to Dπ^-π^+π^-$ decays and determination of the CKM angle $γ$

Published 26 May 2015 in hep-ex | (1505.07044v3)

Abstract: We report a study of the suppressed $B^-\to DK^{-\pi^{+\pi^-$}} and favored $B^-\to D\pi^{-\pi^{+\pi^-$}} decays, where the neutral $D$ meson is detected through its decays to the $K^{{\mp}\pi^{\pm}$} and CP-even $K^{+K^-$} and $\pi^{+\pi^-$} 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 $B^-\to DK^{-\pi^{+\pi^-$}} and favored $B^-\to D\pi^{-\pi^{+\pi^-$}} modes, as well as in the doubly Cabibbo-suppressed $D\to K^{+\pi^-$} final state of the $B^-\to D\pi^{-\pi^{+\pi^-$}} decay. Evidence for the ADS suppressed decay $B^{-}\to DK^{-\pi^{+\pi^-$,}} with $D\to K^{+\pi^-$,} is also presented. From the observed yields in the $B^-\to DK^{-\pi^{+\pi^-$,}} $B^-\to D\pi^{-\pi^{+\pi^-$}} and their charge conjugate decay modes, we measure the value of the weak phase to be $\gamma=(74^{{+20}_{-19})^{\rm} o}$. This is one of the most precise single-measurement determinations of $\gamma$ to date.