Abstract
The theoretical K factor, describing the difference between the leading and higher-order cross sections, can be defined in more than one way. The resulting estimate of the higher-order cross section is sensitive to the order of the fit to the parton densities and the number of loops at which αs is evaluated. We describe alternate ways to define the K factor and show how the definition affects its magnitude and shape for the examples of hadroproduction of Drell-Yan lepton pairs and heavy quarks. We discuss which definition is appropriate under what circumstances.
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