Observation of a new Ξb0 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 Ξb0 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)=6227.1-1.5+1.4±0.5 MeV and Γ(Ξb(6227)0)=18.6-4.1+5.0±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 <30 GeV is measured to be fΞb(6227)0fΞb-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.