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Measurement of $B^{0}_{s}$ and $D^{-}_{s}$ meson lifetimes

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Abstract

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} \rightarrow 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 $B^{0} \rightarrow D^{(*)-}\mu^{+}\nu_\mu$ 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, $\tau^{\rm fs}_{B^{0}_{s}} = 1.547 \pm 0.013 (stat) \pm 0.010 (syst) \pm 0.004 (\tau_{B})$ 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.

Figures and captions

Distributions of $D\mu$ mass for (top panel) reference candidates, formed by combining $ D ^- \rightarrow K^+K^-\pi^-$ candidates with $\mu^+$ candidates, and (bottom panel) signal candidates formed by $ D ^-_ s \rightarrow K^+K^-\pi^-$ candidates combined with $\mu^+$ candidates. The inset shows the $K^+K^-\pi^-$-mass distribution with vertical lines enclosing the $ D ^-$ ( $ D ^-_ s $ ) candidates used to form the reference (signal) candidates. The dark-filled histograms show same-sign candidate distributions.

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Corrected-mass distributions for (top panel) reference $ B ^0 \rightarrow [K^+ K^- \pi^-]_{ D ^{\scalebox{0.4}{(}*\scalebox{0.4}{)}-} } \mu^+ \nu_\mu$ and (bottom panel) signal $ B ^0_ s \rightarrow [K^+K^-\pi^-]_{ D ^{\scalebox{0.4}{(}*\scalebox{0.4}{)}-}_{ s } } \mu^+ \nu_\mu$ candidates satisfying the selection. Results of the global composition-fit are overlaid. In the $ B ^0_ s $ fit projection, the lower- and higher-mass background components described in the text are displayed as a single, merged "physics background" component.

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Ratio between acceptance-corrected yields of signal $ B ^0_ s \rightarrow [K^+K^-\pi^-]_{ D ^{\scalebox{0.4}{(}*\scalebox{0.4}{)}-}_{ s } } \mu^+\nu_\mu$ and reference $ B ^0 \rightarrow [K^+K^-\pi^-]_{ D ^{\scalebox{0.4}{(}*\scalebox{0.4}{)}-} } \mu^+\nu_\mu$ decay yields as a function of (top panel) charm-meson and (middle panel) bottom-meson decay time. The bottom panel shows the ratio between acceptance-corrected $ B ^0$ decay yields in the $[K^+\pi^-\pi^-]_{ D ^{\scalebox{0.4}{(}*\scalebox{0.4}{)}-} } \mu^+\nu_\mu$ and $[K^+K^-\pi^-]_{ D ^{\scalebox{0.4}{(}*\scalebox{0.4}{)}-} } \mu^+\nu_\mu$ channels as a function of $ B ^0$ decay time. Fit results are overlaid. Relevant for the results is only the slope of the ratios as a function of decay time; absolute ratios, which depend on the decay yields, weighting, and efficiencies, are irrelevant.

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Supplementary Material [file]

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Created on 11 December 2018.Citation count from INSPIRE on 18 December 2018.