First measurement of the decay-time-integrated $C\text{\hspace{0.17em}⁣}P$ asymmetry in $B_s^0\to D_s^{-}{\pi }^{+}$ decays

A measurement of the flavour-untagged decay-time-integrated $C\text{\hspace{0.17em}⁣}P$ asymmetry in the flavour-specific decay $B_s^0\to D_s^{-}{\pi }^{+}$, $⟨A_{\mathrm{u}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{g}\mathrm{e}\mathrm{d}}^s⟩$, is performed using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of $13\mathrm{T}\mathrm{e}\mathrm{V}$, corresponding to a total integrated luminosity of $5.4{\mathrm{f}\mathrm{b}}^{-1}$. The $C\text{\hspace{0.17em}⁣}P$ asymmetry is measured in two $D_s^{-}$ meson decay modes, $D_s^{-}\to K^{-}{K}^{+}{\pi }^{-}$ and $D_s^{-}\to {\pi }^{-}{\pi }^{+}{\pi }^{-}$. The combined result, $⟨A_{\mathrm{u}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{g}\mathrm{g}\mathrm{e}\mathrm{d}}^s⟩=(-1.4\pm 5.9(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 1.1(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}))\times {10}^{-3}$, is consistent with the Standard Model expectation and provides a direct constraint on new physics in tree-level $b$-hadron decays.