The Spin Structure of the Nucleon: a phenomenological introduction and the most recent results
After a short hystorical introduction on the understanding of the
structure of the proton and of the neutron, the investigation of the
spin structure of the nucleon via semi- inclusive deep inelastic
scattering on polarized nucleons is updated with the most recent
results of the JLAB, HERMES, and COMPASS experiments.
A short description is given of these experiments, which are complementary
in phase space and use sophisticated and different techniques to polarize
the nucleon targets.
The cases of target spin parallel or orthogonal to the direction of
the incoming lepton require different experimental techniques, have
a different phenomenology and need a different theoretical
After reviewing these differences, the most recent transverse spin
advances are presented, and evidence is given that new properties of
matter at the partonic level have been discovered.