Measurement of the Proton and Deuteron Spin Structure Function g_1 in the Resonance Region

TL;DR

This study measures the proton and deuteron spin structure functions g_1 in the resonance region at low Q^2, providing new insights into their behavior and the evolution of the integral Gamma(Q^2) towards the GDH limit.

Contribution

It presents the first measurements of g_1 in the resonance region at low Q^2 and combines these with deep-inelastic data to analyze the evolution of Gamma(Q^2).

Findings

Significant structure observed in g_1^p in the resonance region.

First data on the low-Q^2 evolution of Gamma(Q^2).

Results approach the Gerasimov-Drell-Hearn limit at Q^2=0.

Abstract

We have measured the proton and deuteron spin structure functions g_1^p and g_1^d in the region of the nucleon resonances for W^2 < 5 GeV^2 and $Q^2\simeq 0.5$ and $Q^2\simeq 1.2$ GeV^2 by inelastically scattering 9.7 GeV polarized electrons off polarized $^{15}NH_3$ and $^{15}ND_3$ targets. We observe significant structure in g_1^p in the resonance region. We have used the present results, together with the deep-inelastic data at higher W^2, to extract $\Gamma(Q^2)\equiv\int_0^1 g_1(x,Q^2) dx$. This is the first information on the low-Q^2 evolution of Gamma toward the Gerasimov-Drell-Hearn limit at Q^2 = 0.