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

Abstract

A description of the virtual photon absorption cross section difference σ_{1/2}-σ_{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

Latex 12 pages, 4 figures. To be published in Phys. Lett. B

References in corpus (4)

• Measurements of the Proton and Deuteron Spin Structure Functions g1 and g2
• Precision Determination of the Neutron Spin Structure Function g1n
• Measurement of the Proton Spin Structure Function g1p with a Pure Hydrogen Target
• The Gerasimov-Drell-Hearn sum rule and the single-pion photoproduction multipole E0+ close to threshold

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