The polarized EMC effect

Conference details: Quark confinement and the hadron spectrum VII : 7th Conference on Quark Confinement and the Hadron Spectrum, QCHS7, Ponta Delgada, Açores, Portugal, 2-7 September 2006 / José Emílio F. T. Ribeiro (ed.): pp. 248-250We calculate both the spin independent and spin dependent nuclear structure functions in an effective quark theory. The nucleon is described as a composite quark-diquark state, and the nucleus is treated in the mean field approximation. We predict a sizable polarized EMC effect, which could be confirmed in future experiments.W. Bentz, I. C. Cloet, and A. W. Thoma

Covariance, Dynamics and Symmetries, and Hadron Form Factors

We summarise applications of Dyson-Schwinger equations to the theory and phenomenology of hadrons. Some exact results for pseudoscalar mesons are highlighted with details relating to the U_A(1) problem. We describe inferences from the gap equation relating to the radius of convergence for expansions of observables in the current-quark mass. We recapitulate upon studies of nucleon electromagnetic form factors, providing a comparison of the ln-weighted ratios of Pauli and Dirac form factors for the neutron and proton.Comment: 9 pages, 2 figures. Contribution to proceedings of Workshop on Exclusive Reactions at High Momentum Transfer, May 21-24, 2007, Jefferson Lab, Newport News, V

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^A_2N / F_2N ratio, that is, the EMC effect. Applying this framework to determine g^A_1p, we find that the ratio g^A_1p / g_1p differs significantly from 1, 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.Comment: 4 pages, 4 figure