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

TL;DR

This study provides precise measurements of the proton and deuteron spin structure functions g2 and asymmetries A2, testing theoretical predictions and sum rules within a broad kinematic range using polarized electron scattering.

Contribution

It presents the first comprehensive measurement of g2p, g2d, A2p, and A2d over a wide kinematic range, and compares results with theoretical models and sum rules.

Findings

g2 approximately follows the twist-2 Wandzura-Wilczek calculation

d2p and d2n are consistent with zero within uncertainties

Data challenge the Burkhardt-Cottingham sum rule without x->0 behavior

Abstract

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 < Q^2 < 20 GeV^2 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 sqrt[R(1+A1)/2] limit.