The Spin Asymmetries of the Nucleon Experiment

The Spin Asymmetries of the Nucleon Experiment (SANE) measured the virtual Compton scattering asymmetries, $A_1$ and $A_2$, from which the spin structure functions of the proton, $g_1$ and $g_2$, can be obtained. The kinematics for these measurements are in a range of Bjorken $x$, $0.3 < x < 0.8$, where extraction of the twist three matrix element $d_2^p $ (an integral with respect to $x$ of $2g_1+ 3g_2$ weighted by $x^2$) is most sensitive. The observable, $d_2$, is a measure of the average restoring Lorentz color force experienced by a quark inside a polarized nucleon after it is struck by a virtual photon in electron Deep Inelastic Scattering (DIS)[1]. The data was taken at the Thomas Jefferson National Accelerator Facility's Hall C, using beam energies of $4.7$ and $5.9~GeV$, probing the nucleon at scales ranging from $Q^2 = 2.5~GeV^2$ up to $Q^2 = 6.5~GeV^2$. In this polarized electron scattering off a polarized proton target experiment two inclusive double spin asymmetries, $A_\parallel$ and $A_{80}$ ($\simeq A_\perp$) were measured using the BETA detector. BETA is a device without magnetic momentum dispersion that consists of a front scintillator hodoscope followed by a threshold gas Cherenkov counter, a Lucite hodoscope and a large array of lead glass detectors. In addition to motivating the physics of the proton's spin structure we shall discuss the analysis and present preliminary results.\\[0pt] [1] M. Burkardt, AIP Conf. Proc. 1149, 62 (2009) [arXiv:0902.0163 [hep-ph]].