Proton spin structure and the axial U(1) problem

Abstract

We emphasise the relation between the spin structure of the proton and the axial U(1) problem. New experiments motivated by the proton spin problem which could shed light on the nature of U(1) symmetry breaking in QCD are discussed.Comment: Invited talk at the Workshop on the Spin Structure of the Proton and Polarized Collider Physics, Trento (July 23-28, 2001), 6 pages, 1 figur