Measurement of the Proton and Deuteron Spin Structure Functiong1in the Resonance Region

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 $W^2<5\mathrm{}{\mathrm{GeV}}^2$ and $Q^2\simeq 0.5$ and $Q^2\simeq 1.2{\mathrm{GeV}}^2$ by inelastically scattering 9.7 GeV polarized electrons off polarized ${}^{15}{\mathrm{NH}}_3$ and ${}^{15}{\mathrm{ND}}_3$ 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 $\gamma \left(Q^2\right)\equiv \int 1^{}{g}_1\left({x,Q}^2\right)\mathrm{dx}$. This is the first information on the low- $Q^2$ evolution of $\gamma$ toward the Gerasimov-Drell-Hearn limit at $Q^2=0\mathrm{}$.