  We report the observation of the doubly strange b baryon Omega_b- in the
decay channel Omega_b- to J/psi Omega-, with J/psi to mu+ mu- and Omega- to
Lambda K-, in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV. Using approximately
1.3 fb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron
Collider, we observe 17.8 +/- 4.9 (stat) +/- 0.8 (syst) Omega_b- signal events
at a mass of 6.165 +/- 0.010 (stat) +/- 0.013(syst.) GeV. The significance of
the observed signal is 5.4 sigma, corresponding to a probability of 6.7 x
10^{-8} of it arising from a background fluctuation.
