Measurement of the Λb cross section and the Λbarb to Λb ratio with J / ψΛ decays in pp collisions at √{ s} = 7 TeV

The Λ_b differential production cross section and the cross section ratio σ (Λbar_b) / σ (Λ_b) are measured as functions of transverse momentum p_T^Λ_b and rapidity |^{y Λ_b} | in pp collisions at √{ s} = 7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on Λ_b decays reconstructed in the exclusive final state J / ψΛ, with the subsequent decays J / ψ →μ⁺μ^- and Λ → pπ, using a data sample corresponding to an integrated luminosity of 1.9fb^-1. The product σ (Λ_b) × B (Λ_b → J / ψΛ) versus p_T^Λ_b falls faster than that of b mesons. The measured value of σ (Λ_b) × B (Λ_b → J / ψΛ) for p_T^Λ_b > 10 GeV and |^{y Λ_b} | < 2.0 is 1.16 ± 0.06 ± 0.12 nb, and the integrated σ (Λbar_b) / σ (Λ_b) ratio is 1.02 ± 0.07 ± 0.09, where the uncertainties are statistical and systematic, respectively.