Measurement of the Neutron Spin Structure Function $g_1^n$ with a Polarized ^3He Target

Abstract

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function $g_1^n(x,Q^2)$ in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized $^3$He internal gas target. The data cover the kinematic range $0.023<x<0.6$ and $1 (GeV/c)^2 < Q^2 <15 (GeV/c)^2$. The integral $\int_{0.023}^{0.6} g_1^n(x) dx$ evaluated at a fixed $Q^2$ of $2.5 (GeV/c)^2$ is $-0.034\pm 0.013(stat.)\pm 0.005(syst.)$. Assuming Regge behavior at low $x$, the first moment $Γ_1^n=\int_0^1 g_1^n(x) dx$ is $-0.037\pm 0.013(stat.)\pm 0.005(syst.)\pm 0.006(extrapol.)$.

Figures (2)

• Figure 1: Schematic diagram of the experimental apparatus (side view).
• Figure 2: The spin asymmetry $A_1^n$ (a) and the spin structure function $g_1^n$ (b) of the neutron as a function of $x$. The values are given for the measured $\left<Q^2\right>$. The error bars are statistical uncertainties. The error bands show the systematic uncertainties. The data points from E-142 have been displaced slightly in $x$ for comparison with the present experiment.