Precision Measurement of the Proton and Deuteron Spin Structure Functions g2 and Asymmetry A2

The authors have measured the spin structure functions g2p and g2d and the virtual photon asymmetries A20 and A2d over the kinematic range 0.02 (le) x (le) 0.8 and 0.7 (le) Q2 (le) 20 GeV2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and 6LiD targets. The measured g2 approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d2p and d2m are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule if there is no pathological behavior as x → 0. The Efremov-Leader-Teryaev integral is consistent with zero within the measured kinematic range. The absolute value of A2 is significantly smaller than the A2 < (√R(1+A2)/2) limit