First Measurement of the Decay-Time-Integrated C P Asymmetry in

A measurement of the flavor-untagged decay-time-integrated C P asymmetry in the flavor-specific decay B s 0 → D s − π + , ⟨ A untagged 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 TeV, corresponding to a total integrated luminosity of 5.4     fb − 1 . The C P asymmetry is measured in two D s − meson decay modes, D s − → K − K + π − and D s − → π − π + π − . The combined result, ⟨ A untagged s ⟩ = ( − 1.4 ± 5.9 ( stat ) ± 1.1 ( syst ) ) × 10 − 3 , is consistent with the Standard Model expectation and provides a direct constraint on new physics in tree-level b -hadron decays.