Measurement of the Λ0b, 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 0 b → J / ψ Λ , Ξ − b → J / ψ Ξ − and Ω − b → J / ψ Ω − signals are observed and the corresponding masses are measured to be M ( Λ 0 b ) = 5619.53 ± 0.13 ( stat . ) ± 0.45 ( syst . ) MeV / c 2 , M ( Ξ − b ) = 5795.8 ± 0.9 ( stat . ) ± 0.4 ( syst . ) MeV / c 2 , M ( Ω − b ) = 6046.0 ± 2.2 ( stat . ) ± 0.5 ( syst . ) MeV / c 2 , while the differences with respect to the Λ 0 b mass are M ( Ξ − b ) − M ( Λ 0 b ) = 176.2 ± 0.9 ( stat . ) ± 0.1 ( syst . ) MeV / c 2 , M ( Ω − b ) − M ( Λ 0 b ) = 426.4 ± 2.2 ( stat . ) ± 0.4 ( syst . ) MeV / c 2 . These are the most precise mass measurements of the Λ 0 b , Ξ − b and Ω − b baryons to date. Averaging the above Λ 0 b mass measurement with that published by LHCb using 35 pb − 1 of data collected in 2010 yields M ( Λ 0 b ) = 5619.44 ± 0.13 ( stat . ) ± 0.38 ( syst . ) MeV / c 2 .