| Summary: | The first measurement of the production rate of Ξ[overline b]⁻ baryons in pp collisions relative to that of Λ[subscript 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<η<6 and p[subscript T]<20 GeV/c, we measure f[subscript Ξ[overline b]⁻]/f[subscript Λ[subscript b]⁰ ] B(Ξ[subscript b]⁻→J/ψΞ⁻)/B(Λ[subscript b]⁰→J/ψΛ)=(10.8±0.9±0.8)×10⁻² √s =7,8 TeV], f [subscript Ξ[subscript b]⁻]/f[subscript Λ[subscript b⁰]B(Ξ[subscript b]⁻→J/ψΞ⁻)/B(Λ[subscript b⁰]→J/ψΛ)=(13.1±1.1±1.0)×10⁻² [√s =13 TeV], where f[subscript Ξ[overline b]⁻] and f[subscript Λ[subscript b⁰]] are the fragmentation fractions of b quarks into Ξ[subscript b]⁻ and Λ[subscript b⁰] baryons, respectively; B represents branching fractions; and the uncertainties are due to statistical and experimental systematic sources. The values of f[subscript Ξ[overline b]⁻]/f [subscript Λ[subscript b⁰] are obtained by invoking SU(3) symmetry in the Ξ[overline b]⁻→J/ψΞ⁻ and Λ[subscript b⁰]→J/ψΛ decays. Production asymmetries between Ξ[overline b]⁻ and Ξ[overline b]⁺ baryons are also reported. The mass of the Ξ[overline b]⁻ baryon is also measured relative to that of the Λ[subscript b⁰] baryon, from which it is found that m(Ξ[overline b]⁻)=5796.70±0.39±0.15±0.17 MeV/c², where the last uncertainty is due to the precision on the known Λ[subscript b⁰] mass. This result represents the most precise determination of the Ξ[overline b]⁻mass.
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