The Gerasimov-Drell-Hearn Sum Rule

Abstract

In the confinement regime at Q^2=0 the Gerasimov-Drell-Hearn (GDH) Sum Rule connects static properties of the nucleon with the difference of spin dependent doubly polarized total absorption cross sections of real photons. Now, for the first time this fundamental sum rule is verified by the GDH-Collaboration with circularly polarized real photons and longitudinally polarized nucleons at the two accelerators ELSA and MAMI. The integral (sum) of the GDH Sum Rule can be generalized to the case of virtual photons. This allows to establish a Q^2 dependency and to study the transition to the perturbative regime of QCD. Ultimately, the GDH Sum Rule can be related to the Bjorken and the Ellis-Jaffe Sum Rule. This contribution covers the status of theory concerning the GDH Sum Rule as well as the experimental approaches and their results for the absorption of real and virtual photons. We point out that the so-called No-Subtraction hypothesis, often considered the weakest part of the derivation of the GDH Sum Rule, in fact follows from unitarity and does not impair the fundamental character of the GDH Sum Rule. The shown experimental data verify the GDH Sum Rule for the proton at the level of 8% including the systematic uncertainties from extrapolations to unmeasured energy regions. For the GDH Sum Rule on the neutron and the isovector case we find unexpected contributions at photon energies above 1 GeV.

In press at Progress in Particle and Nuclear Physics

References in corpus (7)

• Big Bang Nucleosynthesis (in "The Review of Particle Properties" 2004)
• Measurement of the Proton Spin Structure Function $g_1(x,Q^2)$ for $Q^2$ from 0.15 to 1.6 GeV${}^2$ with CLAS
• Spin Asymmetry and Gerasimov-Drell-Hearn Sum Rule for the Deuteron
• The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Nucleon
• The $Q^2$-dependence of the generalised Gerasimov-Drell-Hearn integral for the deuteron, proton and neutron
• Spin Response of the Nucleon in the Resonance Region
• Status of the RHIC Spin Program

Cited by in corpus (21)

• Baryon spectroscopy
• Progress Toward Understanding Baryon Resonances
• Nucleon Polarizabilities: from Compton Scattering to Hydrogen Atom
• Determination of the Proton Spin Structure Functions for 0.05 < Q^2 < 5 GeV^2 using CLAS
• First measurement of the helicity asymmetry for $\gamma p\to p{\pi }^0$ in the resonance region
• Expanding Nuclear Physics Horizons with the Gamma Factory
• Hadron structure at low Q^2
• Precise Determination of the Deuteron Spin Structure at Low to Moderate $Q^2$ with CLAS and Extraction of the Neutron Contribution
• Measurement of the Bjorken Sum at very low $Q^2$
• Dispersion Theory in Electromagnetic Interactions
• Measurement of the Q^2 Dependence of the Deuteron Spin Structure Function g_1 and its Moments at Low Q^2 with CLAS
• Measurement of the generalized spin polarizabilities of the neutron in the low $Q^2$ region
• Evaluation of the forward Compton scattering off protons: II. Spin-dependent amplitude and observables
• Helicity-dependent reaction \vec γ\vec d\to πNN and its contribution to the GDH sum rule for the deuteron
• Updating spin-dependent Regge intercepts
• Polarizabilities of the nucleon and spin dependent photo-absorption
• Gamow-Teller transitions and the spin EMC effect: the Bjorken sum-rule in medium
• Single-pion contribution to the Gerasimov--Drell--Hearn sum rule and related integrals
• Measurement of the nucleon spin structure functions for 0.01<$Q^2$<1 GeV${}^2$ using CLAS
• The Gerasimov-Drell-Hearn sum-rule with nuclear targets
• Coupled-channel contributions to the GDH sum rule from the Jülich-Bonn approach