Spin-Dependent Structure Functions in Nuclear Matter and the Polarized EMC Effect

An excellent description of both spin-independent and spin-dependent quark distributions and structure functions has been obtained with a modified Nambu—Jona-Lasinio model, which is free of unphysical thresholds for nucleon decay into quarks—hence incorporating an important aspect of confinement. We utilize this model to investigate nuclear medium modifications to structure functions and find that we are readily able to reproduce both nuclear matter saturation and the experimental F_2N^A/F_2N ratio, that is, the European Muon Collaboration (EMC) effect. Applying this framework to determine g_1p^A, we find that the ratio g_1p^A/g_1p differs significantly from unity, with the quenching caused by the nuclear medium being about twice that of the spin-independent case. This represents an exciting result, which, if confirmed experimentally, will reveal much about the quark structure of nuclear matter.