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 sqrt[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.
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