The first measurement of the production rate of $\Xi_b^$ baryons in $pp$ collisions relative to that of $\Lambda_b^0$ baryons is reported, using data samples collected by the LHCb experiment, and corresponding to integrated luminosities of $1$, $2$ and $1.6$ fb$^{1}$ at $\sqrt{s}=7, 8$ and $13$ TeV, respectively. In the kinematic region $2 < \eta < 6$ and $p_{\rm T}<20$ GeV/$c$, we measure \begin{align*} \frac{f_{\Xi_b^}}{f_{\Lambda_b^0}}\frac{{\mathcal{B}}(\Xi_b^\to J/\psi\Xi^)}{{\mathcal{B}}(\Lambda_b^0\to J/\psi\Lambda)} &= (10.8\pm0.9\pm0.8)\times10^{2} [\sqrt{s}=7,8 {\rm TeV}],\\ \frac{f_{\Xi_b^}}{f_{\Lambda_b^0}}\frac{{\mathcal{B}}(\Xi_b^\to J/\psi\Xi^)}{{\mathcal{B}}(\Lambda_b^0\to J/\psi\Lambda)} &= (13.1\pm1.1\pm1.0)\times10^{2} [\sqrt{s}=13 {\rm TeV}], \end{align*} where $f_{\Xi_b^}$ and $f_{\Lambda_b^0}$ are the fragmentation fractions of $b$ quarks into $\Xi_b^$ and $\Lambda_b^0$ baryons, respectively, ${\mathcal{B}}$ represents branching fractions, and the uncertainties are due to statistical and experimental systematic sources. The values of $f_{\Xi_b^}/f_{\Lambda_b^0}$ are obtained by invoking SU(3) symmetry in the $\Xi_b^\to J\psi\Xi^$ and $\Lambda_b^0\to J/\psi\Lambda$ decays. Production asymmetries between $\Xi_b^$ and $\bar{\Xi}_b^+$ baryons are also reported. The mass of the $\Xi_b^$ baryon is also measured relative to that of the $\Lambda_b^0$ baryon, from which it is found that \begin{align*} m(\Xi_b^) &= 5796.70\pm0.39\pm0.15\pm0.17 {\rm MeV}/c^2, \end{align*} \noindent where the last uncertainty is due to the precision on the known $\Lambda_b^0$ mass. This result represents the most precise determination of the $\Xi_b^$ mass.
Invariantmass distributions for (top) $\Lambda ^0_ b \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \Lambda $ candidates, (middle) $\Xi ^_ b \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \Xi ^ $, $\Xi ^ \rightarrow \Lambda \pi^_{\rm L}$, and (bottom) $\Xi ^_ b \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \Xi ^ $, $\Xi ^ \rightarrow \Lambda \pi^_{\rm D}$. The subscript on the $\pi ^ $ refers to whether the corresponding track is long or downstream. The left column shows the combined 7 and 8 $\text{\,TeV}$ data and the right one shows the 13 $\text{\,TeV}$ data. The fitted probability distributions functions (PDF) are overlaid. 
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Animated gif made out of all figures. 
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Fitted signal yields and peak position of the $\Lambda ^0_ b $ signal peak, as obtained from the fit described in the text. The subscript on the $\pi ^ $ refers to whether the corresponding track is long or downstream. The uncertainties shown are statistical only. 
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Selection efficiencies as obtained from the simulation of $\Lambda ^0_ b \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \Lambda $ and $\Xi ^_ b \rightarrow { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \Xi ^ $, $\Xi ^ \rightarrow \Lambda \pi^_{\rm L}$ decays at $\sqrt{s}=7,\,8$ $\text{\,TeV}$ and 13 $\text{\,TeV}$ . The efficiencies ($\epsilon$) listed are those associated with the detector acceptance (acc), the reconstruction and selection (sel) the trigger (trig), their product, and the relative efficiency. 
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Yields of $\Lambda ^0_ b $ and $\Xi ^_ b $ decays, split by the charge of the final state, and their asymmetries, for the combined 7, 8 $\text{\,TeV}$ data samples and the 13 $\text{\,TeV}$ data sample. Uncertainties are statistical only. 
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Summary of relative systematic uncertainties on the production ratio $R$. 
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Created on 20 February 2019.Citation count from INSPIRE on 21 February 2019.