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

We present a determination of the strong coupling constant α_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 Zp_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 α_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 α_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 (N³LO and beyond) from half the shift between the NLO and NNLO α_s values, finding Δαsth=0.0011.