Measurements of the proton and deuteron spin structure functions g1 and g2

Abstract

Measurements are reported of the proton and deuteron spin structure functions gp1 and gd1 at beam energies of 29.1, 16.2, and 9.7 GeV, and gp2 and gd2 at a beam energy of 29.1 GeV. The integrals Γp = ∫10gp1(x,Q2)dx and Γd = ∫10gd1(x,Q2)dx were evaluated at fixed Q2 = 3(GeV/c)2 using the full data set to yield Γp = 0.132±0.003(stat)±0.009(syst) and Γd = 0.047±0.003±0.006. The Q2 dependence of the ratio g1/F1 was studied and found to be small for Q2 > 1 (GeV/c)2. Within experimental precision the g2 data are well described by the twist-2 contribution, gWW2. Twist-3 matrix elements were extracted and compared to theoretical predictions. The asymmetry A2 was measured and found to be significantly smaller than the positivity limit √R for both proton and deuteron targets. Ap2 is found to be positive and inconsistent with zero. Measurements of g1 in the resonance region show strong variations with x and Q2, consistent with resonant amplitudes exited from unpolarized data. These data allow us to study the Q2 dependence of the integrals Γp and Γn below the scaling region.