Study of Double Spin Asymmetries in Inclusive ep Scattering at Jefferson Lab

Abstract

The spin structure of the proton has been investigated in the high Bjorken x and low momentum transfer Q^2 region. We used Jefferson Lab's polarized electron beam, a polarized target, and a spectrometer to get both the parallel and perpendicular spin asymmetries A_para and A_perp. These asymmetries produced the physics asymmetries A_1 and A_2 and spin structure functions g_1 and g_2. We found Q^2 dependences of the asymmetries at resonance region and higher-twist effects. Our result increases the available data on the proton spin structure, especially at resonance region with low Q^2. Moreover, A_2 and g_2 data show clear Q^2 evolution, comparing with RSS and SANE-BETA. Negative resonance in A_2 data needs to be examined by theory. It can be an indication of very negative transverse-longitudinal interference contribution at W ~ 1.3 GeV. Higher twist effect appears at the low Q^2 of 1.9 GeV^2, although it is less significant than lower Q^2 data of RSS. Twist-3 matrix element d_2 was calculated using our asymmetry fits evaluated at Q^2 = 1.9 GeV^2. d_2 = -0.0087 +- 0.0014 was obtained by integrating 0.47 <= x <= 0.87.