Measurement of the Neutron Spin Structure Function g2n and Asymmetry A2n

TL;DR

This study measured the neutron's spin-dependent structure functions g2n and asymmetry A2n over a broad kinematic range, providing insights into nucleon spin structure and testing theoretical predictions like Wandzura-Wilczek.

Contribution

First measurement of g2n and A2n over extensive kinematic range using polarized electron scattering from polarized helium-3, testing theoretical models and extracting twist-3 matrix elements.

Findings

A2n significantly below the positivity limit.

g2n data consistent with Wandzura-Wilczek prediction.

Estimated twist-3 matrix element d2n and integral of g2n.

Abstract

We have measured the neutron structure function g$_{2}^{n}$ and the virtual photon-nucleon asymmetry A$_{2}^{n}$ over the kinematic range $0.014\leq x \leq 0.7$ and $1.0 \leq Q^{2} \leq 17.0$ by scattering 48.3 GeV longitudinally polarized electrons from polarized $^{3}$He. Results for A$_{2}^{n}$ are significantly smaller than the $\sqrt{R}$ positivity limit over most of the measured range and data for g$_2^{n}$ are generally consistent with the twist-2 Wandzura-Wilczek prediction. Using our measured g$_{2}^{n}$ we obtain results for the twist-3 reduced matrix element $d_{2}^{n}$, and the integral $\int$g$_{2}^{n}(x)dx$ in the range $0.014\leq x \leq 1.0$. Data from this experiment are combined with existing data for g$_{2}^{n}$ to obtain an average for $d_{2}^{n}$ and the integral $\int$g$_{2}^{n}(x)dx$.