Q² evolution of ³He spin structure functions moments

Abstract

Sum rules offer the opportunity to test our understanding of the structure of a system on general grounds. In this paper we investigate the ³He nucleus using the Gerasimov-Drell-Hearn and Burkhardt-Cottingham sum rules. We have previously used the polarized ³He target measurements to extract the neutron spin structure, our goal here is to investigate rather the ³He nucleus. We have determined for the first time the Q² evolution of $\Gamma_1(Q^2)=\int_0^{1} g_1(x,Q^2) dx$ and $\Gamma_2(Q^2)=\int_0^1 g_2(x,Q^2) dx$ for ³He in the range 0.1 GeV² ≤ Q² ≤ 0.9 GeV² with good precision. Γ₁(Q²) displays a smooth variation from high to low Q². However, we do not see yet its expected turnover toward the real photon limit value. On the other hand the Burkhardt-Cottingham sum rule holds at all measured Q²s within uncertainties due mainly to cancellations between the elastic, quasielastic and the Δ(1232) resonance contributions.