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

Abstract We present a determination of the strong coupling constant $$\alpha _s(m_Z)$$ αs(mZ) 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 $$p_T$$ pT 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 $$\alpha _s$$ αs 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 $$\alpha _s(m_Z) = 0.1185 \pm 0.0005^\text {(exp)}\pm 0.0001^\text {(meth)}$$ αs(mZ)=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 (N$$^3$$ 3 LO and beyond) from half the shift between the NLO and NNLO $$\alpha _s$$ αs values, finding $$\Delta \alpha ^\mathrm{th}_s =0.0011$$ Δαsth=0.0011