Precision determination of alphas using an unbiased global NLO parton set
Abstract
We determine the strong coupling alphas from a next-to-leading order analysis of processes used for the NNPDF2.1 parton determination, which includes data from neutral and charged current deep-inelastic scattering, Drell-Yan and inclusive jet production. We find alphas(MZ)=0.1191+-0.0006 (exp), where the uncertainty includes all statistical and systematic experimental uncertainties, but not purely theoretical uncertainties. We study the dependence of the results on the dataset, by providing further determinations based respectively on deep-inelastic data only, and on HERA data only. The deep-inelastic fit gives the consistent result alphas(MZ)=0.1177+-0.0009(exp), but the result of the HERA-only fit is only marginally consistent. We provide evidence that individual data subsets can have runaway directions due to poorly determined PDFs, thus suggesting that a global dataset is necessary for a reliable determination.
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