Observation of a new Ξ0 b 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 Ξ0 b resonance decaying to the Ξ− b πþ final state is presented. The state, referred to as Ξbð6227Þ0, has a measured mass and natural width of mðΞbð6227Þ0Þ ¼ 6227:1þ1.4 −1.5 0.5 MeV and ΓðΞbð6227Þ0Þ ¼ 18:6þ5.0 −4.1 1.4 MeV, where the uncertainties are statistical and systematic. The production rate of the Ξbð6227Þ0 state relative to that of the Ξ− b baryon in the kinematic region 2 < η < 5 and pT < 30 GeV is measured to be fΞbð6227Þ0 fΞ− b BðΞbð6227Þ0 → Ξ− b πþÞ ¼ 0.045 0.008 0.004; where BðΞbð6227Þ0 → Ξ− b πþÞ is the branching fraction of the decay, and fΞbð6227Þ0 and fΞ− b represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed Ξbð6227Þ− 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.