Calculations of Single-inclusive Cross Sections and Spin Asymmetries in Pp Scattering∗

Single-inclusive reactions in pp scattering, such as pp → γX , pp → πX , pp → jetX , play an important role in QCD. At sufficiently large produced transverse momentum, pT , QCD perturbation theory (pQCD) can be used to derive predictions for these reactions. Since high pT implies large momentum transfer, the cross section may be factorized at leading power in pT into convolutions of long-distance pieces representing the structure of the initial hadrons, and parts that are short-distance and describe the hard interactions of the partons. The long-distance contributions are universal, that is, they are the same in any inelastic reaction, whereas the shortdistance pieces depend only large scales and, therefore, can be evaluated using QCD perturbation theory. Because of this, single-inclusive cross sections offer unique possibilities to probe the structure of the initial hadrons in ways that are complementary to deeply-inelastic scattering. At the same time, they test the perturbative framework, for example, the relevance of higher orders in the perturbative expansion and of power-suppressed contributions to the cross section.