Measurements of the Proton and Deuteron Spin Structure Function g2 and Asymmetry A2

TL;DR

This study measures the spin structure functions g2 and asymmetries A2 for protons and deuterons across a range of x and Q2, providing insights into nucleon spin structure and testing theoretical models.

Contribution

It presents new measurements of g2 and A2 for proton and deuteron, including twist-3 matrix elements, expanding understanding of nucleon spin dynamics.

Findings

A2 asymmetries are smaller than the positivity limit.

g2 data agree with twist-2 g2WW predictions.

Extracted twist-3 matrix elements compared to theory.

Abstract

We have measured proton and deuteron virtual photon-nucleon asymmetries A2p and A2d and structure functions g2p and g2d over the range 0.03<x<0.8 and 1.3<Q2<10 (GeV/c)2 by inelastically scattering polarized electrons off polarized ammonia targets. Results for A2 are significantly smaller than the positivity limit sqrt(R) for both targets. Within experimental precision, the g2 data are well-described by the twist-2 contribution g2WW. Twist-3 matrix elements have been extracted and are compared to theorectical predictions.