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The $Q^2$-dependence of the generalised Gerasimov-Drell-Hearn integral for the deuteron, proton and neutron

HERMES collaboration·A. Airapetian
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Abstract

The Gerasimov-Drell-Hearn (GDH) sum rule connects the anomalous contribution to the magnetic moment of the target nucleus with an energy-weighted integral of the difference of the helicity-dependent photoabsorption cross sections. The data collected by HERMES with a deuterium target are presented together with a re-analysis of previous measurements on the proton. This provides a measurement of the generalised GDH integral covering simultaneously the nucleon-resonance and the deep inelastic scattering regions. The contribution of the nucleon-resonance region is seen to decrease rapidly with increasing $Q^2$. The DIS contribution is sizeable over the full measured range, even down to the lowest measured $Q^2$. As expected, at higher $Q^2$ the data are found to be in agreement with previous measurements of the first moment of $g_1$. From data on the deuteron and proton, the GDH integral for the neutron has been derived and the proton--neutron difference evaluated. This difference is found to satisfy the fundamental Bjorken sum rule at $Q^2 = 5$ GeV$^2$.

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HERMES collaboration, A. Airapetian. 2002-10-18. The $Q^2$-dependence of the generalised Gerasimov-Drell-Hearn integral for the deuteron, proton and neutron. https://doi.org/10.1140/epjc%2Fs2002-01118-x

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