Observation of the Ωb- baryon and measurement of the properties of the Ξb- and Ωb- baryons

Abstract

We report the observation of the bottom, doubly-strange baryon Ωb- through the decay chain Ωb-→J/ψΩ-, where J/ψ→μ+μ-, Ω-→ΛK-, and Λ→pπ-, using 4.2 fb-1 of data from pp̅ collisions at √s=1.96 TeV, and recorded with the Collider Detector at Fermilab. A signal is observed whose probability of arising from a background fluctuation is 4.0×10-8, or 5.5 Gaussian standard deviations. The Ωb- mass is measured to be 6054.4±6.8(stat)±0.9(syst) MeV/c2. The lifetime of the Ωb- baryon is measured to be 1.13-0.40+0.53(stat)±0.02(syst) ps. In addition, for the Ξb- baryon we measure a mass of 5790.9±2.6(stat)±0.8(syst) MeV/c2 and a lifetime of 1.56-0.25+0.27(stat)±0.02(syst) ps. Under the assumption that the Ξb- and Ωb- are produced with similar kinematic distributions to the Λb0 baryon, we find σ(Ξb-)B(Ξb-→J/ψΞ-)/σ(Λb0)B(Λb0→J/ψΛ)=0.167-0.025+0.037(stat)±0.012(syst) and σ(Ωb-)B(Ωb-→J/ψΩ-)/σ(Λb0)B(Λb0→J/ψΛ)=0.045-0.012+0.017(stat)± 0.004(syst) for baryons produced with transverse momentum in the range of 6–20 GeV/c.