Measurement of the proton $A_1$ and $A_2$ spin asymmetries. Probing Color Forces

Abstract

The Spin Asymmetries of the Nucleon Experiment (SANE) measured the proton spin structure function g 2 in a range of Bjorken x, 0.3 < x < 0.8, where extraction of the twist-3 matrix element d p 2 (an integral of g 2 weighted by x 2) is most sensitive. The data was taken from Q 2 equal to 2.5 GeV 2 up to 6.5 GeV 2. In this polarized electron scattering off a polarized hydrogen target experiment, two double spin asymmetries, A and A ⊥ were measured using the BETA (Big Electron Telescope Array) Detector. BETA consisted of a scintillator hodoscope, gasČerenkov counter, lucite hodoscope and a large lead glass electromagnetic calorimeter. With a unique open geometry, a threshold gasČerenkov detector allowed BETA to cleanly identify electrons for this inclusive experiment. A measurement of d p 2 is compared to lattice QCD calculations.

The extraction of the spin structure function, g2 (and g1) at low Bjorken x

“…Plots of these results are shown in Figure 6.5, Figure 6.6 and Figure 6.7 [56]. SANE shows good agreement with world data at large W .…”

“…Shown in Figure 6.10 and Figure 6.9 are the results of g 1 and g 2 [56]. They where extracted as described in section (4.5).…”