Measurement of the Λ_b^0, Ξ_b^- and Ω_b^- baryon masses

Abstract

Bottom baryons decaying to a J/ψ meson and a hyperon are reconstructed using 1.0 fb^{-1} of data collected in 2011 with the LHCb detector. Significant Λ_b^0 \rightarrow J/ψΛ, Ξ_b^-\rightarrow J/ψΞ^- and Ω_b^- \rightarrow J/ψΩ^- signals are observed and the corresponding masses are measured to be M(Λ_b^0) = 5619.53 \pm 0.13 (stat) \pm 0.45 (syst) MeV/c^2, M(Ξ_b^-) = 5795.8 \pm 0.9 (stat) \pm 0.4 (syst) MeV/c^2, M(Ω_b^-) = 6046.0 \pm 2.2 (stat) \pm 0.5 (syst) MeV/c^2, while the differences with respect to the Λ_b^0 mass are M(Ξ_b^-)-M(Λ_b^0) = 176.2 \pm 0.9 (stat) \pm 0.1 (syst) MeV/c^2, M(Ω_b^-)-M(Λ_b^0) = 426.4 \pm 2.2 (stat) \pm 0.4 (syst) MeV/c^2. These are the most precise mass measurements of the Λ_b^0, Ξ_b^- and Ω_b^- baryons to date. Averaging the above Λ_b^0 mass measurement with that published by LHCb using 35 pb^{-1} of data collected in 2010 yields M(Λ_b^0) = 5619.44 \pm 0.13 (stat) \pm 0.38 (syst) MeV/c^2.

9 pages, 2 figures, to be submitted to Physical Review Letters