Parton spin asymmetries in polarized hadrons at high energies

Abstract

The predictions of perturbative QCD for the evolution of quark and gluon distributions for polarized hadrons, in general, and for polarized protons, in particular, are developed. Analytical and numerical studies suggest that quark and gluon polarizations increase with increasing energy at fixed Feynman x. Moreover, the average gluon asymmetry grows as ln Q 2 receiving contributions from both quark and gluon asymmetries at lower energy. This has important implications for the growth of orbital angular momenta of partons and presents a challenge to model building. A new sum rule for a particular moment of the quark and gluon asymmetries is derived. We conclude that more work is needed to determine how useful polarized proton beams might be in the search for and exploration of new physics in lepton-proton, p p and pp colliders.