Highlights of JLab Neutron (He-3) Spin Program

Nucleon spin structure has been an active, exciting and intriguing subject of interest for the last three decades. Recent precision spin-structure data from Jefferson Lab have significantly advanced our knowledge of nucleon structure at low Q(2). In particular, it has improved our understanding of spin sum rules and higher-twist effects. First, results of neutron spin sum rules and polarizabilities in the low to intermediate Q(2) region are presented. Comparison with theoretical calculations, in particular with Chiral Perturbation Theory (ChPT) calculations, are discussed. Surprising disagreements of ChPT calculations with experimental results on the generalized spin polarizability, delta(n)(LT), were found. Results of precision measurements of the g(2) structure function to study higher-twist effects are presented. The data indicate a significant higher-twist (twist-3 or higher) effect. The second moment of the spin structure functions and the twist-3 matrix element d(2) results were extracted. The high Q(2) result was compared with a Lattice QCD calculation. Finally, other neutron spin structure results, such as the resonance data for quark-hadron duality study and a precision measurement of the neutron spin asymmetry in the valence quark (high-x) region are briefly discussed.