Precision measurement of the proton and deuteron spin structure functions g2 and asymmetries A2

We have measured the spin structure functions g2p and g2d and the virtual photon asymmetries A2p and A2d over the kinematic range 0.02⩽x⩽0.8 and 0.7⩽Q2⩽20GeV2 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 d2p and d2n 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 our measured kinematic range. The absolute value of A2 is significantly smaller than the A2<R(1+A1)/2 limit.