Total Top-Quark Pair-Production Cross Section at Hadron Colliders Through O (αS4)

We compute the next-to-next-to-leading order (NNLO) quantum chromodynamics ( QCD) correction to the total cross section for the reaction gg -> t (t) over bar + X. Together with the partonic channels we computed previously, the result derived in this Letter completes the set of NNLO QCD corrections to the total top pair- production cross section at hadron colliders. Supplementing the fixed order results with soft- gluon resummation with next- to- next- to- leading logarithmic accuracy, we estimate that the theoretical uncertainty of this observable due to unknown higher order corrections is about 3% at the LHC and 2.2% at the Tevatron. We observe a good agreement between the standard model predictions and the available experimental measurements. The very high theoretical precision of this observable allows a new level of scrutiny in parton distribution functions and new physics searches.