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 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 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 ^mathrm{th}_s =0.0011.
Highlights
We present a determination of the strong coupling constant αs(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 pT distributions using exact NNLO theory
The correlated replica method is akin to the standard NNPDF methodology in that it starts by producing a set of replicas of the original data, but uses these to construct a set of correlated αs-dependent PDF replicas, the c-replicas, which correspond to parameters θ (k)(αs) when k runs over the replica sample and αs takes a number of discrete values
In this work we have presented a new determination of the strong coupling constant αs (m Z ) jointly with a global determination of PDFs which, by relying on NNPDF3.1, for the first time includes a large amount of LHC data using exact NNLO theory in all cases
Summary
As discussed in the introduction, the αs determination presented here differs from our previous one [17,18] because the value of αs and its uncertainty are determined from a correlated fit together with the PDFs. After briefly summarizing the main aspects of the NNPDF methodology and the way it was used to determine αs in Ref. [17,18], we describe the main idea of the new method, and discuss the details of its implementation. The salient aspects of the NNPDF methodology will be recalled here; the reader is referred to the original literature [16], of which we follow the notation, and references therein) and recent reviews [2,21,22] for a more detailed discussion The salient aspects of the NNPDF methodology will be recalled here; the reader is referred to the original literature (see Ref. [16], of which we follow the notation, and references therein) and recent reviews [2,21,22] for a more detailed discussion
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