Double-spin asymmetries and absolute cross sections were measured at large Bjorken x ð0.25 ≤ x ≤ 0.90Þ, in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized 3 He target. In this dedicated experiment, the spin structure function g 3 He 2 was determined with precision at large x, and the neutron twist-3 matrix element d n 2 was measured at hQ 2 i of 3.21 and 4.32 GeV 2 =c 2 , with an absolute

We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element d 2 of the neutron (d n 2 ) was conducted. The quantity d n 2 represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. This color force was determined from a linear combination of the third moments of the 3 He spin structure functions, g 1 and g 2 , after nuclear corrections had been applied to these moments. The structure functions were obtained from a measurement of the unpolarized cross section and of double-spin asymmetries in the scattering of a longitudinally polarized electron beam from a transversely and a longitudinally polarized 3 He target. The measurement kinematics included two average Q 2 bins of 3.2 GeV 2 and 4.3 GeV 2 , and Bjorken-x 0.25 ≤ x ≤ 0.90 covering the deep inelastic and resonance regions. We have found that d n 2 is small and negative for hQ 2 i ¼ 3.2 GeV 2 , and even smaller for hQ 2 i ¼ 4.3 GeV 2 , consistent with the results of a lattice QCD calculation. The twist-4 matrix element f n 2 was extracted by combining our measured d n 2 with the world data on the first moment in x of g n 1 , Γ n 1 . We found f n 2 to be roughly an order of magnitude larger than d n 2 . Utilizing the extracted d n 2 and f n 2 data, we separated the Lorentz color force into its electric and magnetic components, F y;n E and F y;n B , and found them to be equal and opposite in magnitude, in agreement with the predictions from an instanton model but not with those from QCD sum rules. Furthermore, using the measured double-spin asymmetries, we have extracted the virtual photon-nucleon asymmetry on the neutron A n 1 , the structure function ratio g n 1 =F n 1 , and the quark ratios ðΔu þ ΔūÞ=ðu þūÞ and ðΔd þ ΔdÞ=ðd þdÞ. These results were found to be consistent with deep-inelastic scattering world data and with the prediction of the constituent quark model but at odds with the perturbative quantum chromodynamics predictions at large x.

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