NNPDF3.1notop alphas

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

Summary

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 \alpha_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 \pm 0.0005^\text{(exp)}\pm 0.0001^\text{(meth)}, showing that methodological uncertainties are negligible. We conservatively estimate the theoretical uncertainty due to missing higher order QCD corrections (N^3LO and beyond) from half the shift between the NLO and NNLO \alpha_s values, finding \Delta\alpha^{\rm th}_s =0.0011.

Paper: arXiv:1802.03398

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