| We discuss several issues related to collinear singularities and the choice of the factorization scale in perturbative QCD calculations. First, we argue in favor of the use of a bottom-quark distribution function, which sums collinear logarithms, in the calculation of the cross section for Higgs-boson production in association with bottom quarks. As a testing ground for Higgs searches, we propose a measurement of Z-boson production in association with heavy quarks, using an inclusive heavy-quark tagging technique. Next, we present a calculation of the next-to-leading-order QCD corrections to Drell-Yan production of a W boson, regulating the collinear singularities with a nonzero quark mass and the infrared and ultraviolet singularities with dimensional regularization. Finally, we present the collinear factorization scheme, in which only collinear physics is absorbed into the parton distribution functions. We provide a physically motivated method for choosing the factorization scale in this scheme, and show, for the case of Drell-Yan production of an electroweak gauge boson, that the next-to-leading-order QCD corrections are very small for this choice of factorization scale. |
