Parton Distribution Functions (PDFs) are a necessary ingredient in the calculation of cross sections at collider experiments with hadron beams. This chapter explores the techniques of determining the PDFs and their uncertainties, based on global analyses of data sets arising from a variety of hard-scattering processes. PDFs are determined at leading order, next-to-leading order, and next-to-next-to-leading order, with the corresponding orders of hard coefficients and evolution. Differences in the PDFs of different orders, and in their uncertainties, are described. Combinations of PDFs from different global fitting groups are discussed, and several useful tools for comparisons of PDFs are described.
Next-to-leading order hard scattering using fully unintegrated parton distribution functions
