Measurement of $B^0_s$ and $D^-_s$ meson lifetimes

We report on a measurement of the flavor-specific $B^0_s$ lifetime and of the $D^-_s$ lifetime using proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to 3.0  $fb^{−1}$ of integrated luminosity. Approximately 407 000 $B^0_s \to D^{(*)-}_s \mu^+\nu_{\mu}$ decays are partially reconstructed in the $K^+ K^- \pi^- \mu^+$ final state. The $B^0_s$ and $D^-_s$ natural widths are determined using, as a reference, kinematically similar $B^0_s \to D^{(*)-}_s \mu^+\nu_{\mu}$ decays reconstructed in the same final state. The resulting differences between widths of $B^0_s$ and $B^0$ mesons and of $D^-_s$ and $D^-$ mesons are $\Delta_{\Gamma}(B) = −0.0115 \pm 0.0053 (stat) \pm 0.0041 (syst)  ps^{-1}$ and $\Delta_{\Gamma}(D) = 1.0131 \pm 0.0117 (stat) \pm 0.0065 (syst)  ps^{-1}$, respectively. Combined with the known $B^0$ and $D^-$ lifetimes, these yield the flavor-specific $B^0_s$ lifetime, $\tau^{fs}_{B^0_s} = 1.547 \pm 0.013 (stat) ± 0.010 (syst) ± 0.004 (\tau_B)  ps$ and the $D^-_s$ lifetime, $\tau_{D^-_s} = 0.5064 \pm 0.0030 (stat) \pm 0.0017 (syst) \pm 0.0017 (\tau_D)$ ps. The last uncertainties originate from the limited knowledge of the $B^0$ and $D^−$ lifetimes. The results improve upon current determinations.