Studies of nucleon spin structure at HERMES

The HERMES experiment studies the spin structure of the nucleon using polarized semi-inclusive deep-inelastic positron scattering and polarized quasi-real photoproduction. Previous analyses of nucleon spin structure combine inclusive deep-inelastic scattering data and measured hyperon decay constants assuming $SU(3)flavor$ symmetry; asymmetries in the processes studied at HERMES may constrain nucleon spin structure more directly. Results are discussed for quark polarizations extracted from semi-inclusive deep-inelastic scattering asymmetries, for gluon polarization extracted from the asymmetry of high-$pT$ hadron pairs, and for the first observation of single-spin azimuthal asymmetries in pion production.