Recent HERMES results from inclusive and semi-inclusive hadron production

Abstract

HERMES collected a wealth of data using the 27.6 GeV polarized HERA lepton beam and various pure, polarized and unpolarized, gaseous targets. This unique data set opens the door to various measurements sensitive to the multi-dimensional structure of the nucleon. Among them are two-hadron production in semi-inclusive deep-inelastic scattering on a transversely polarized target, providing access to different transverse-momentum-dependent distribution and fragmentation functions in a way complementary to single-hadron production. Also transverse-target single-spin asymmetries in inclusive electroproduction of charged pions and kaons have been recently extracted, complementing data from proton-proton collisions, where large, so far unexplained, asymmetries have been observed. From inclusive measurements on various nuclear targets, the Lambda polarization is extracted, also here complementing measurements in proton-proton collisions.