Observation of the Ω-b and Measurement
of the Properties of the
Ξ-b  and Ω-b











CDF observes the production of the Ω-b through the decay chain Ω-b → J/ψ Ω-, J/ψ → μ+μ-, Ω-→Λ K-, Λ → p π-.  The data was collected in 4.2 fb-1 of collisions.
Illustration of the final state
An illustration of the decay chain



J/&psi &Xi and J/&psi &Omega mass distributions

J/ψ Ξ- and J/ψ Ω- mass distributions.

The properties of the Ξ-b  and Ω-b are measured within a comprehensive program of b-hadron studies, which provide a control sample for the understanding of the systematic effects that are important to the measurements.  The following properties have been obtained:




Mass (MeV/c2)
Lifetime (ps)
Ξ-b 5790.9 ± 2.6 ± 0.8
1.56+0.27-0.25 ± 0.02
Ω-b 6054.4 ± 6.8 ± 0.9
1.13+0.53-0.40 ± 0.02


The mass measurement of the Ξ-b updates our previous measurement, made with a 1.9 fb-1 data sample1.  The lifetime measurement of the Ξ-b is the first ever made with a fully reconstructed final state.

The mass measurement of the Ω-b is inconsistent with the only previous observation of this particle2.  The lifetime measurement of the Ω-b is the first ever obtained.

A comparison between the mass measurements and several theoretical predicitions is summarized below:

Theory/experiment comparison

The relative rates of production of the two particles are measured with respect to the Λb, since it is the only b-baryon for which a large sample is available.  The measurement is made with the assumption that the production kinematics of the Ξ-b  and Ω-b are identical to that of the Λb.  The ratios of cross section times branching fractions are

Xi_b rate ratio
Omega_b rate ratio


Details can be obtained from a recent seminar and the paper in the following links:

Special Joint Experimental-Theoretical Seminar (19 May 2009)
Paper available at arXiv:0905.3123

1.  T. Aaltonen et al. (CDF Collaboration), Phys. Rev. Lett. 99, 052002 (2007)
2.  V. M. Abazov et. al. (D0 Collaboration), Phys. Rev. Lett. 101, 232002 (2008).