Exploring the Nucleon Structure: From Lepton Scattering to Hadron Beams

Since the middle of the last century, it has been known that nucleons are not point-like elementary particles, like electrons, but have an internal structure. They consist of a complex system of quarks and gluons, which are all interacting with each other and moving relative to each other, following the rules of quantum chromodynamics. Many of the basic properties of the nucleon, like the origin of its spin- and polarization-effects, but also the pressure distribution within the nucleon, can be understood based on the knowledge of the space- and momentum-distributions of the partons. These distributions can be described with different types of distribution functions, like Generalized Parton Distributions (GPDs) and Transverse Momentum-dependent Distribution functions (TMDs). Experimentally, these functions can be accessed by deep inelastic electron scattering experiments, but also in a complementary kinematic regime by the annihilation or scattering of hadronic beams. The talk will review recent developments in the field and discuss perspectives for nucleon structure studies at FAIR and other places.