ABSTRACT:
The quantity *d*_{2}, written as an *x*^{2}-weighted moment of a linear combination of the spin structure functions *g*_{1} and *g*_{2}, has the interpretation of being the average transverse Lorentz color force felt by a quark immediately following its interaction with a virtual photon in the deep inelastic scattering (DIS) process due to the remnant di-quark
system. It has been calculated in different nucleon structure models and in lattice QCD, where it is seen to be small and negative for *Q*^{2} > 4 GeV^{2}. The existing measurement for the matrix element *d*_{2} on the neutron from the combined data of SLAC E155 and Jefferson Lab E99-117 at *Q*^{2} = 5 GeV^{2} disagrees with the lattice QCD calculation by almost two standard deviations. This discrepancy served as the motivation for the E06-014 experiment in Hall A of Jefferson Lab. Double-spin asymmetries and unpolarized cross sections were measured in the scattering of a longitudinally polarized electron beam of energies 4.74 and 5.89 GeV from a longitudinally and transversely polarized ^{3}He target, covering the DIS and resonance regions characterized by 0:25 < *x* < 0:90
and 2 ≤ *Q*^{2} ≤ 7 GeV^{2}. This allowed for the extraction of *d*^{n}_{2} matrix element in two ⟨*Q*^{2}⟩ bins of 3.21 and 4.32 GeV^{2}. Additionally, the virtual photon-nucleon asymmetry *A*^{n}_{1}
was extracted, along with the evaluation of the polarized-to-unpolarized quark ratios
Δ*u ⁄ u* and Δ*d ⁄ d*. The matrix element *a*_{2} is also obtained from our *g*_{1} data. We present the results of our measurements, which are compared to the world data and various theoretical models and lattice QCD calculations. Future plans to measure *d*^{n}_{2} and *A*^{n}_{1} with the upgrade of Jefferson Lab will be discussed. |