Uncertainty induced by QCD coupling in the CTEQ global analysis of parton distributions

Hung-Liang Lai; Joey Huston; Zhao Li; Pavel Nadolsky; Jon Pumplin; Daniel Stump; C. -P. Yuan

doi:10.1103/PhysRevD.82.054021

paper

Uncertainty induced by QCD coupling in the CTEQ global analysis of parton distributions

arXiv:1004.4624 · doi:10.1103/PhysRevD.82.054021

Abstract

We examine the dependence of parton distribution functions (PDFs) on the value of the QCD coupling strength $α_{s} (M_{Z})$ . We explain a simple method that is rigorously valid in the quadratic approximation normally applied in PDF fitting, and fully reproduces the correlated dependence of theoretical cross sections on $α_{s}$ and PDF parameters. This method is based on a statistical relation that allows one to add the uncertainty produced by $α_{s}$ , computed with some special PDF sets, in quadrature with the PDF uncertainty obtained for the fixed $α_{s}$ value (such as the CTEQ6.6 PDF set). A series of four CTEQ6.6AS PDFs realizing this approach, for $α_{s}$ values in the interval $0.116 \leq α_{s} (M_{Z}) \leq 0.120$ , is presented. Using these PDFs, the combined $α_{s}$ and PDF uncertainty is assessed for theoretical predictions at the Fermilab Tevatron and Large Hadron Collider.

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Uncertainty induced by QCD coupling in the CTEQ global analysis of parton distributions

Abstract

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