Measurements of the $Q^2$-Dependence of the Proton and Neutron Spin Structure Functions g1p and g1n

Abstract

The structure functions g1p and g1n have been measured over the range 0.014 < x < 0.9 and 1 < Q2 < 40 GeV2 using deep-inelastic scattering of 48 GeV longitudinally polarized electrons from polarized protons and deuterons. We find that the Q2 dependence of g1p (g1n) at fixed x is very similar to that of the spin-averaged structure function F1p (F1n). From a NLO QCD fit to all available data we find $Γ_1^p - Γ_1^n =0.176 \pm 0.003 \pm 0.007$ at Q2=5 GeV2, in agreement with the Bjorken sum rule prediction of 0.182 \pm 0.005.

Figures (3)

• Figure 1: Ratios $g_1^p/F_1^p$ extracted from experiments assuming the $g_2^{WW}$ model for $g_2$. Inner errors are statistical only, while systematic errors are included in quadrature in the outer error bars. The solid curves correspond to the NLO QCD fit described in the text, while the dashed curves are from the simple fit given by Eq. 5.
• Figure 2: Same as Fig. 1 except for $g_1^n/F_1^n$ and Eq. 6 for the dashed curves.
• Figure 3: Data for $g_1^p$ (a), $g_1^n$ (b), and $g_1^p - g_1^n$ (c), evaluated at $Q^2=5$ GeV$^2$. The data are from this experiment (solid circles), E143 (open circles), SMC (squares), HERMES (stars), and E154 (crosses). The $g_1^p - g_1^n$ values were obtained from the proton and deuteron results of E155, E143, and SMC, while the proton E155 and neutron E154 results were used to obtain the results with the cross symbol. The curves are as in Figs. 1 and 2.