Observation of a new Ξ0b state

Abstract

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 Ξ0b resonance decaying to the Ξb- π+ final state is presented. The state, referred to as Ξb(6227)0, has a measured mass and natural width of m(Ξb(6227)0)= 6227:1+1.4−1.5+-0.5 MeV and Γ(Ξb(6227)0) =18,6+5.0−4.1+-1.4 MeV, where the uncertainties are statistical and systematic. The production rate of the Ξb(6227)0 state relative to that of the Ξb− baryon in the kinematic region 2 < η < 5 and pT < 30 GeV is measured to be fΞb(6227)0/fΞb−B(Ξb(6227)0→Ξb−π+)=0.045+-0.008+-0.004; where B(Ξb(6227)0 → Ξb−π+) is the branching fraction of the decay, and fΞb(6227)0 and fΞb− represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed Ξb(6227)− state, along with the mass of the Ξb− baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.