Single-Spin/Azimuthal Asymmetries In Semi-Inclusive And Exclusive Dis

Recent measurements of pion production in deeply inelastic scattering of positrons have revealed azimuthal distributions of the pions that are proportional to the polarization of only the target nucleon. Such spin-azimuthal asymmetries from semiinclusive measurements can be interpreted in terms of previously unobserved quark distribution functions related to transversity, which represents the probability of finding a transversely polarized quark in a nucleon polarized transverse to its (infinite)) momentum. Much larger asymmetries have now been seen in the exclusive kinematic limit. Their interpretation is more problematic.