Observation of two new Ξb- Baryon resonances

Abstract

Two structures are observed close to the kinematic threshold in the Ξ 0 b π − mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb − 1 , recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content b d s are expected in this mass region: the spin-parity J P = ( 1 / 2 ) + and J P = ( 3 / 2 ) + states, denoted Ξ ' − b and Ξ * − b . Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be m ( Ξ ' − b ) − m ( Ξ 0 b ) − m ( π − ) = 3.653 ± 0.018 ± 0.006 MeV / c 2 , m ( Ξ * − b ) − m ( Ξ 0 b ) − m ( π − ) = 23.96 ± 0.12 ± 0.06 MeV / c 2 , Γ ( Ξ * − b ) = 1.65 ± 0.31 ± 0.10 MeV , where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of Γ ( Ξ ' − b ) < 0.08 MeV at 95% confidence level. Relative production rates of these states are also reported.