Quark spin distribution and quark-antiquark annihilation in single-spin hadron-hadron collisions

We show that quark-antiquark annihilation processes in single-spin inclusive production experiments can yield useful information on hadron spin structure in general, and provide crucial tests for the existence of orbiting valence quarks in particular. There are several experimental indications and theoretical arguments for the existence of such orbital motion inside polarized protons or antiprotons. Simple relations between quark-spin distributions and left-right asymmetries in such production processes can be given, and quantitative predictions can be made.