Study of the production of Λ_b⁰ and B-bar⁰ hadrons in pp collisions and first measurement of the Λ_b⁰→J/ψpK^- branching fraction

The product of the Λ_b⁰(B-bar⁰) differential production cross-section and the branching fraction of the decay Λ_b⁰→J/ψpK^-(B-bar⁰→J/ψK-bar^*(892)⁰) is measured as a function of the beauty hadron transverse momentum, p_T, and rapidity, y. The kinematic region of the measurements is p_T < 20 GeV/c and 2.0 < y < 4.5. The measurements use a data sample corresponding to an integrated luminosity of 3fb^-1 collected by the LHCb detector in pp collisions at centre-of-mass energies √s=7 TeV in 2011 and √s=8 TeV in 2012. Based on previous LHCb results of the fragmentation fraction ratio, f_Λb⁰/f_d, the branching fraction of the decay Λ_b⁰→J/ψpK^- is measured to be B(Λ_b⁰→J/ψpK^-)=(3.17 ± 0.04 ± 0.07 ± 0.34_-0.28^+0.45) × 10^-4 where the first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the branching fraction of the decay B-bar⁰→J/ψK-bar^*(892)⁰, and the fourth is due to the knowledge of f_Λb⁰/f_d. The sum of the asymmetries in the production and decay between Λ_b⁰ and Λ-bar_b⁰ is also measured as a function of p_T and y. The previously published branching fraction of Λ_b⁰→J/ψpπ^-, relative to that of Λ_b⁰→J/ψpK^-, is updated. The branching fractions of Λ_b⁰→P_c⁺(→J/ψp)K^- are determined. (authors)