Transversity measurement at HERMES

Abstract

Abstract Polarised deep-inelastic lepton scattering has been the main experimental basis for our understanding of the spin structure of the nucleon. In addition to inclusive and semi-inclusive measurements, recently single-spin azimuthal asymmetries in semi-inclusive scattering have been recognized as a powerful tool to access further information about the spin structure of the nucleon. The appearance of non-zero single-spin asymmetries can be explained in terms of a non-zero transversity distribution combined with a non-zero Collins fragmentation function. Results from the HERMES experiment are presented on single-spin asymmetries in semi-inclusive hadron production from longitudinally polarised hydrogen and deuterium targets. The azimuthal dependence of the asymmetries is discussed in relation to the transversity distribution and the data are compared with a number of theoretical calculations.