Precision determination of the strong coupling constant within a global PDF analysis

We present a determination of the strong coupling constant alpha(s) (m(Z)) based on the NNPDF3.1 determination of parton distributions, which for the first time includes constraints from jet production, top-quark pair differential distributions, and the Z p(T) distributions using exact NNLO theory. Our result is based on a novel extension of the NNPDF methodology - the correlated replica method - which allows for a simultaneous determination of a s and the PDFs with all correlations between them fully taken into account. We study in detail all relevant sources of experimental, methodological and theoretical uncertainty. At NNLO we find alpha(s) (m(Z)) = 0.1185 +/- 0.0005((exp)) +/- 0.0001((meth)), showing that methodological uncertainties are negligible. We conservatively estimate the theoretical uncertainty due to missing higher order QCD corrections ((NLO)-L-3 and beyond) from half the shift between the NLO and NNLO alpha(s) values, finding Delta alpha s(th) = 0.0011.