Measurement of $C\text{\hspace{0.17em}⁣}P$ observables in $B^{\pm }\to D^{(\ast )}{K}^{\pm }$ and $B^{\pm }\to D^{(\ast )}{\pi }^{\pm }$ decays using two-body $D$ final states

Measurements of $C\text{\hspace{0.17em}⁣}P$ observables in $B^{\pm }\to D^{(\ast )}{K}^{\pm }$ and $B^{\pm }\to D^{(\ast )}{\pi }^{\pm }$ decays are presented, where $D^{(\ast )}$ indicates a neutral $D$ or $D^{\ast }$ meson that is an admixture of meson and anti-meson states. Decays of the $D^{\ast }$ meson to the $D{\pi }^0$ and $D\gamma$ final states are partially reconstructed without inclusion of the neutral pion or photon. Decays of the $D$ meson are reconstructed in the $K^{\pm }{\pi }^{\mp }$, $K^{+}{K}^{-}$, and ${\pi }^{+}{\pi }^{-}$ final states. The analysis uses a sample of charged $B$ mesons produced in proton-proton collisions and collected with the LHCb experiment, corresponding to integrated luminosities of 2.0, 1.0, and 5.7 fb${}^{-1}$ taken at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The measurements of partially reconstructed $B^{\pm }\to D^{\ast }{K}^{\pm }$ and $B^\pm \to D^* \pi^\pm$with$D \to K^\mp \pi^\pm$ decays are the first of their kind, and a first observation of the $B^{\pm }\to (D{\pi }^0{)}_{D^{\ast }}{\pi }^{\pm }$ decay is made with a significance of 6.1 standard deviations. All $C\text{\hspace{0.17em}⁣}P$ observables are measured with world-best precision, and in combination with other LHCb results will provide strong constraints on the CKM angle $\gamma$.