First observation and amplitude analysis of the $B^{-}\to D^{+}{K}^{-}{\pi }^{-}$ decay

The $B^{-}\to D^{+}{K}^{-}{\pi }^{-}$ decay is observed in a data sample corresponding to $3.0{\mathrm{f}\mathrm{b}}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. Its branching fraction is measured to be ${\cal B}(B^{-}\to D^{+}K^{-}\pi^{-}) = (7.31 \pm 0.19 \pm 0.22 \pm 0.39) \times 10^{-5}$ where the uncertainties are statistical, systematic and from the branching fraction of the normalisation channel $B^{-}\to D^{+}\pi^{-}\pi^{-}$, respectively. An amplitude analysis of the resonant structure of the $B^{-}\to D^{+}{K}^{-}{\pi }^{-}$ decay is used to measure the contributions from quasi-two-body $B^{-}\to D_0^{\ast }(2400{)}^0{K}^{-}$, $B^{-}\to D_2^{\ast }(2460{)}^0{K}^{-}$, and $B^{-}\to D_J^{\ast }(2760{)}^0{K}^{-}$ decays, as well as from nonresonant sources. The $D_J^{\ast }(2760{)}^0$ resonance is determined to have spin~1.