Spin Dependent Nucleon Structure at Intermediate Q

This thesis focuses on hadronic spin structure at low and intermediate energies, 0 < Q2 < 3 GeV 2. The thesis is divided into two main sections. Each section addresses a different aspect of spin dependent hadronic physics which has not been studied previously in detail. The first section studies hydrogen hyperfine splitting. A polarizability term depending on the proton's G1 and G2 spin dependent structure functions is extracted with a theoretical precision of 0.1 ppm. A detailed reanalysis of the elastic form factor contributions is performed. Important radiative recoil corrections are calculated for the first time. Weak interaction effects are examined and are found to contribute only marginally at the current level of precision. A pion electroproduction parameterization of the existing low energy data data is constructed. The analysis yields a polarizability correction consistent with the value extracted from hyperfine splitting, but quantitative comparison of the extracted polarizability will require data from CEBAF. The second section studies the effect of higher twists or 1/Q 2 corrections to the lowest moments of the proton's structure functions. The target mass corrections to the moments of the spin dependent scaling functions gl and g2 are derived. The twist-four corrections to the first moment of G1 are examined and the magnitude of the effect estimated using the MIT bag model. A continuous parameterization of the moment from low to high Q 2 is constructed. The resulting prediction should be compared with experiment. The interplay between resonance structure and twist corrections at low Q2 is studied using the spin independent structure function F2 . The twist-four corrections along with estimates of the radiative corrections are extracted from existing data. The analogous analysis for the spin dependent structure functions awaits experimental data. Thesis Supervisor: Xiangdong Ji Title: Professor Nature resolves everything into its component atoms and never reduces anything to nothing. -Lucretius, (c.100 c.55 B.C.)