Measurement of the virtual-photon asymmetry A2 and the spin-structure function g2 of the proton

TL;DR

This paper reports measurements of the proton's virtual-photon asymmetry A2 and spin-structure function g2 over a broad kinematic range, confirming sum rule predictions and providing insights into proton spin structure.

Contribution

It presents new experimental data on A2 and g2 of the proton from the HERMES experiment, extending previous measurements and testing theoretical sum rules.

Findings

Results are consistent with previous CERN and SLAC data.

The integral of g2(x) supports the Burkhardt-Cottingham sum rule.

The twist-3 contribution to g2 is compatible with zero.

Abstract

A measurement of the virtual-photon asymmetry A_2(x,Q^2) and of the spin-structure function g_2(x,Q^2) of the proton are presented for the kinematic range 0.004 < x < 0.9 and 0.18 GeV^2 < Q^2 < 20 GeV^2. The data were collected by the HERMES experiment at the HERA storage ring at DESY while studying inclusive deep-inelastic scattering of 27.6 GeV longitudinally polarized leptons off a transversely polarized hydrogen gas target. The results are consistent with previous experimental data from CERN and SLAC. For the x-range covered, the measured integral of g_2(x) converges to the null result of the Burkhardt-Cottingham sum rule. The x^2 moment of the twist-3 contribution to g_2(x) is found to be compatible with zero.