Showing papers by "Daniel R. Stump published in 2010"

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

Abstract: We examine the dependence of parton distribution functions (PDFs) on the value of the QCD coupling strengths(MZ). 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 ons and PDF parameters. This method is based on a statistical relation that allows one to add the uncertainty produced bys, computed with some special PDF sets, in quadrature with the PDF uncertainty obtained for the fixeds value (such as the CTEQ6.6 PDF set). A series of four CTEQ6.6AS PDFs realizing this approach, fors values in the interval 0.116 � �s(MZ) � 0.120, is presented. Using these PDFs, the combineds and PDF uncertainty is assessed for theoretical predictions at the Fermilab Tevatron and Large Hadron Collider.

Parton distributions for event generators

Abstract: In this paper, conventional global QCD analysis is generalized to produce parton distribution functions (PDFs) optimized for use with event generators at the Large Hadron Collider (LHC). This optimization is accomplished by complementing usual constraints on the PDFs from the existing hard-scattering experimental data with those needed to reproduce cross sections for key scattering processes at the LHC, as predicted by the best available theory, in the joint input to the global analysis. With the optimized PDFs, predictions obtained by event generators at a given order in the QCD coupling strength reproduce the representative LHC cross sections computed at one higher order. In the present study, the optimized PDFs for leading-order event generators were developed. Several optimization strategies and resulting candidate PDF sets (labeled as CT09MCS, CT09MC1 and CT09MC2) are compared with those from other approaches.