Observation of a new Ξb0 state

Using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 8.5     fb − 1 , the observation of a new excited Ξ 0 b resonance decaying to the Ξ − b π + final state is presented. The state, referred to as Ξ b ( 6227 ) 0 , has a measured mass and natural width of m ( Ξ b ( 6227 ) 0 ) = 6227 . 1 + 1.4 − 1.5 ± 0.5     MeV and Γ ( Ξ b ( 6227 ) 0 ) = 18 . 6 + 5.0 − 4.1 ± 1.4     MeV , where the uncertainties are statistical and systematic. The production rate of the Ξ b ( 6227 ) 0 state relative to that of the Ξ − b baryon in the kinematic region 2 < η < 5 and p T < 30     GeV is measured to be f Ξ b ( 6227 ) 0 f Ξ − b B ( Ξ b ( 6227 ) 0 → Ξ − b π + ) = 0.045 ± 0.008 ± 0.004 , where B ( Ξ b ( 6227 ) 0 → Ξ − b π + ) is the branching fraction of the decay, and f Ξ b ( 6227 ) 0 and f Ξ − b represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed Ξ b ( 6227 ) − state, along with the mass of the Ξ − b baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.