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 Λ0b→J/ψΛ, Ξ−b→J/ψΞ− and Ω−b→J/ψΩ− signals are observed and the corresponding masses are measured to be M(Λ0b)=5619.53±0.13(stat.)±0.45(syst.) MeV/c2, M(Ξ−b)=5795.8±0.9(stat.)±0.4(syst.) MeV/c2, M(Ω−b)=6046.0±2.2(stat.)±0.5(syst.) MeV/c2, while the differences with respect to the Λ0b mass are M(Ξ−b)−M(Λ0b)=176.2±0.9(stat.)±0.1(syst.) MeV/c2, M(Ω−b)−M(Λ0b)=426.4±2.2(stat.)±0.4(syst.) MeV/c2. These are the most precise mass measurements of the Λ0b, Ξ−b and Ω−b baryons to date. Averaging the above Λ0b mass measurement with that published by LHCb using 35 pb−1 of data collected in 2010 yields M(Λ0b)=5619.44±0.13(stat.)±0.38(syst.) MeV/c2.