BDT classifier output for the signal and background. Both training and test samples are shown; their definitions are given in the text.

Fits to the invariant mass spectrum of (a) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} pK^-$ and (b) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi^+K^-$ combinations. The $\Lambda ^0_ b $ and $\overline{ B }{} ^0$ signals are shown by the (magenta) solid curves. The (black) dotted lines are the combinatorial backgrounds, and the (blue) solid curves show the totals. In (a) the $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+K^-$ and $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi^+K^-$ reflections, caused by particle misidentification, are shown with the (brown) dot-dot-dashed and (red) dot-dashed shapes, respectively, and the (green) dashed shape represents the doubly misidentified $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^{+}\overline{p}$ final state, where the kaon and proton masses are swapped. In (b) the $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi^+K^-$ mode is shown by the (red) dashed curve and the (green) dot-dashed shape represents the $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p K ^- $ reflection.

Invariant mass distributions of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} pK^-$ data candidates in the sideband regions $60-200$ MeV on either side of the $\Lambda ^0_ b $ mass peak, reinterpreted as misidentified (a) $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+K^-$ and (b) $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi^+ K ^- $ combinations through appropriate mass reassignments. The (red) dashed curves show the $\overline{ B }{} ^0 $ contributions and the (green) dot-dashed curves show $\overline{ B }{} ^0_ s $ contributions. The (black) dotted curves represent the polynomial background and the (blue) solid curves the total.

(a) Decay time acceptances (arbitrary scale) from simulation for (green) circles $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} pK^-$, and (red) open-boxes $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{ K }{} ^{*0} (892)$ decays. (b) Ratio of the decay time acceptances between $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} pK^-$ and $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{ K }{} ^{*0} (892)$ decays obtained from simulation. The (blue) line shows the result of the linear fit.

Decay time distributions for $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} pK^-$ shown as (blue) circles, and $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{ K }{} ^{*0} (892)$ shown as (green) squares. For most entries the error bars are smaller than the points.

Decay time ratio between $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} pK^-$ and $\overline{ B }{} ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{ K }{} ^{*0} (892)$ decays, and the fit for $\Delta_{\Lambda B}$ used to measure the $\Lambda ^0_ b $ lifetime.

Animated gif made out of all figures.

Systematic uncertainties on the $\Delta_{\Lambda B}$, the lifetimes ratio $\tau_{\Lambda ^0_ b }/\tau_{\overline{ B }{} ^0 }$ and the $\Lambda ^0_ b $ lifetime. The systematic uncertainty associated with $\Delta_{\Lambda B}$ is independent of the $\overline{ B }{} ^0 $ lifetime.