Probing QCD with top-quark pairs at CMS

The inclusive cross section for top-pair production as measured by the CMS experiment in proton- proton collisions at a center-of-mass of 7 TeV at the LHC is compared to the QCD prediction at highest order available, using various sets of parton distribution functions. For each parton distribution set, the pole mass of the top quark, and the strong coupling constant, are extracted. This extraction provides an important test of the mass scheme applied in Monte Carlo simulations and gives complementary information, with different sensitivity to theoretical and experimental uncertainties, than direct measurements of top-quark mass. The determined strong coupling is in a good agreement with the world average. This is the first determination of the strong coupling using top-quark production