The distributions of two-jet event shapes contain information onhadronization in QCD. Near the two-jet limit, these distributions can bedescribed by convolutions of nonperturbative event shape functions with thesame distributions calculated in resummed perturbation theory. The shapefunctions, in turn, are determined by correlations of momentum flow operatorswith each other and with light-like Wilson lines, which describe the couplingof soft, wide-angle radiation to jets. We observe that leading powercorrections to the mean values of event shapes are determined by thecorrelation of a single momentum flow operator with the relevant Wilson lines.This generalizes arguments for the universality of leading power correctionsbased on the low-scale behavior of the running coupling or resummation. We alsoshow how a study of the angularity event shapes can provide information oncorrelations involving multiple momentum flow operators, giving a window to thesystem of QCD dynamics that underlies the variety of event shape functions. Inderiving these results, we review, develop and compare factorization techniquesin conventional perturbative QCD and soft-collinear effective theory (SCET). Wegive special emphasis to the elimination of double counting of momentum regionsin these two formalisms.
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