First Observation of Excited Omega(-)(b) States

Abstract

We report four narrow peaks in the Ξ0bK− mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb−1 recorded by the LHCb experiment. Referring to these states by their mass, the mass values are m[Ωb(6316)−]=6315.64±0.31±0.07±0.50 MeV, m[Ωb(6330)−]=6330.30±0.28±0.07±0.50 MeV, m[Ωb(6340)−]=6339.71±0.26±0.05±0.50 MeV, m[Ωb(6350)−]=6349.88±0.35±0.05±0.50 MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Ξ0b mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be Γ[Ωb(6316)−]<2.8 MeV, Γ[Ωb(6330)−]<3.1 MeV and Γ[Ωb(6340)−]<1.5 MeV. The natural width of the Ωb(6350)− peak is 1.4+1.0−0.8±0.1 MeV, which is 2.5σ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6σ to 7.2σ. After accounting for the look-elsewhere effect, the significances of the Ωb(6316)− and Ωb(6330)− peaks are reduced to 2.1σ and 2.6σ, respectively, while the two higher mass peaks exceed 5σ. The observed peaks are consistent with expectations for excited Ω−b resonances.