Observation of a New Ξ_b^- Resonance

From samples of pp collision data collected by the LHCb experiment at sqrt[s]=7, 8 and 13 TeV, corresponding to integrated luminosities of 1.0, 2.0 and 1.5  fb^-1, respectively, a peak in both the Λ_b^0K^- and Ξ_b^0π^- invariant mass spectra is observed. In the quark model, radially and orbitally excited Ξ_b^- resonances with quark content bds are expected. Referring to this peak as Ξ_b(6227)^-, the mass and natural width are measured to be m_Ξ_b(6227)^-=6226.9±2.0±0.3±0.2  MeV/c^2 and Γ_Ξ_b(6227)^-=18.1±5.4±1.8  MeV/c^2, where the first uncertainty is statistical, the second is systematic, and the third, on m_Ξ_b(6227)^-, is due to the knowledge of the Λ_b^0 baryon mass. Relative production rates of the Ξ_b(6227)^-→Λ_b^0K^- and Ξ_b(6227)^-→Ξ_b^0π^- decays are also reported.