Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron

TL;DR

This study measures the deep inelastic scattering contribution to the Gerasimov-Drell-Hearn integral for protons and neutrons, providing data that supports QCD predictions and suggests minimal higher twist effects.

Contribution

It provides the first measurement of the deep inelastic contribution to the GDH integral for the proton and neutron, clarifying their roles in the full integral and testing QCD predictions.

Findings

The proton's contribution to the GDH integral is significant.

Data are consistent with next-to-leading order QCD fits.

Higher twist effects are not prominently observed.

Abstract

The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised 1H and 3He internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant.