The Spin Structure Function g2
Stephen E Rock · AIP conference proceedings · 2003
Abstract. We have measured the spin structure functions g p2 and g d 2 over the kinematic range 0.02≤ x ≤ 0.8 and 0.7≤Q2 ≤ 20 GeV2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and 6LiD targets. Our measured g2 approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d p2 and d n 2 are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule. The Efremov-Leader-Teryaev integral is consistent with zero within our measured kinematic range. The deep-inelastic spin structure functions of the nucleons, g1(x,Q2) and g2(x,Q2), depend on the spin distribution of the partons and their correlations. The function g1 can be primarily understood in terms of the quark parton model (QPM) and perturbative QCD with higher twist terms at low Q2. The function g2 is of particular interest since it has contributions from quark-gluon correlations and other higher twist terms at leading order in Q2 which cannot be described perturbatively. By interpreting g2 using the operator product expansion (OPE) [1, 2], it is possible to study contributions to the nucleon spin structure beyond the simple QPM. The structure function g2 can be written [3]: g2(x,Q2) = gWW2 (x,Q2)+g2(x,Q2) where gWW2 (x,Q2) =−g1(x,Q2)+