A measurement of the flavour-untagged decay-time-integrated ${ C\!P}$ asymmetry in the flavour-specific decay ${ B_s^0 \to D_s^-\pi^+}$, ${ \langle A^s_{ \rm untagged}\rangle}$, is performed using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of ${ 13\,{ \rm TeV}}$, corresponding to a total integrated luminosity of ${ 5.4\,{ \rm fb}^{ -1}}$. The ${ C\!P}$ 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, $\langle A^s_{ \rm untagged}\rangle = ( -1.4 \pm 5.9\,\rm{ (stat)} \pm 1.1\,\rm{ (syst)}) \times 10^{ -3}$, is consistent with the Standard Model expectation and provides a direct constraint on new physics in tree-level $b$-hadron decays.
Categories: hep-ex