Nucleon spin structure

Nucleons (protons and neutrons) are spin=1/2 subatomic particles, composed of quarks. In the late 1980s, the European Muon Collaboration conducted experiments that evidenced that the spin carried by the quarks is not sufficient to justify the total spin of the nucleons.

The research on these topics has been continued by the Spin Muon Collaboration (SMC) at CERN, by HERMES at DESY, by COMPASS  at CERN, and others.