Parameterisation of \sigma_{1/2}-\sigma_{3/2} for Q^2 \geq 0 and non-resonance contribution to the GDH sum rule

TL;DR

This paper develops a Regge-based parameterisation of the virtual photon absorption cross section difference for protons and neutrons, fitting extensive DIS data to evaluate non-resonance contributions to the GDH sum rule across various Q^2 values.

Contribution

It introduces a new parameterisation method based on Regge theory that accurately describes cross section data and predicts contributions to the GDH sum rule for both real and virtual photons.

Findings

The parameterisation reliably fits the experimental data.

It provides smooth Q^2-transition predictions for photo-production.

The non-resonance contribution explains a significant part of the GDH sum rule discrepancy.

Abstract

A description of the virtual photon absorption cross section difference \sigma_{1/2}-\sigma_{3/2} for the proton and the neutron is obtained with a parameterisation based on a Regge type approach. The parameterisation is obtained from global fits to the cross section data derived from the spin asymmetries measured in DIS of longitudinally polarised leptons from polarised ^1H, ^3He and ^2H targets in the range 0.3 GeV^2 < Q^2 < 70 GeV^2 and 4 GeV^2 < W^2 < 300 GeV^2. The fits give a reliable description of the data and provide predictions for the photo-production through a smooth Q^2-transition. The contribution above the resonance region to the Gerasimov-Drell-Hearn sum rule for real and virtual photons has been evaluated. For the real photons this contribution accounts for a large fraction of the discrepancy between the sum rule expectations and the single pion photo-production analysis estimates