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

TL;DR

This paper determines the strong coupling constant $oldsymbol{_s}$ using a global PDF analysis with novel correlated replica methodology, incorporating new experimental constraints and detailed uncertainty analysis, achieving a precise NNLO result.

Contribution

It introduces a new correlated replica method for simultaneous determination of $_s$ and PDFs, fully accounting for correlations and uncertainties in a global analysis.

Findings

_s(m_Z) = 0.1185  0.0005 (exp)  0.0001 (meth)

Methodological uncertainties are negligible.

Estimated theoretical uncertainty due to missing higher orders is 0.0011.

Abstract

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$^3$LO and beyond) from half the shift between the NLO and NNLO $\alpha_s$ values, finding $\Delta\alpha^{\rm th}_s =0.0011$.