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 d2 of the neutron (dn2) was conducted. The quantity dn2 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 3He spin structure functions, g1 and g2, 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 3He target. The measurement kinematics included two average Q2 bins of 3.2 GeV2 and 4.3 GeV2, and Bjorken-x 0.25 ≤ x ≤ 0.90 covering the deep inelastic and resonance regions. We have found that dn2 is small and negative for ⟨Q2⟩ = 3.2 GeV2, and even smaller for ⟨Q2⟩ = 4.3 GeV2, consistent with the results of a lattice QCD calculation. The twist-4 matrix element fn2 was extracted by combining our measured dn2 with the world data on the first moment in x of gn1, Γn1. We found fn2 to be roughly an order of magnitude larger than dn2 . Utilizing the extracted dn2 and fn2 data, we separated the Lorentz color force into its electric and magnetic components, Fy,nE and Fy,nB, 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 An1, the structure function ratio gn1/Fn1, and the quark ratios (Δu + Δu¯)/(u + u¯) and (Δd + Δd¯)/(d + d¯). 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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This material is based upon work supported by the U.S. Department of Energy (DOE) Office of Science under Awards No. DE-FG02-94ER40844 and No. DE-FG02-87ER40315. Jefferson Lab is operated by the Jefferson Science Associates, LLC, under DOE Grant No. DE-AC05-060R23177.
See Supplemental Material at http://link.aps.org/supplemental/10.1103/PhysRevD.94.052003 for raw data files containing tables of all results (and their uncertainties) reported.
Flay, D.; Posik, M.; Parno, D. S.; Allada, Kalyan C.; Armstrong, W. R.; Averett, T.; Benmokhtar, F.; Bertozzi, W.; Camsonne, A.; Canan, M.; Cates, G. D.; Chen, C.; Chen, J. -P.; Choi, S.; Chudakov, E.; Cusanno, F.; Dalton, M. M.; Deconinck, W.; de Jager, C. W.; Deng, X.; Deur, A.; Dutta, Chiranjib; El Fassi, L.; Franklin, G. B.; Friend, M.; Gao, H.; Garibaldi, F.; Gilad, S.; Gilman, R.; Glamazdin, O.; Kolarkar, Ameya Suresh; and Korsch, Wolfgang, "Measurements of dn2 and An1: Probing the Neutron Spin Structure" (2016). Physics and Astronomy Faculty Publications. 433.
results_asym_He-3.txt (3 kB)
results_asym_n.txt (1 kB)
results_color-forces.txt (1 kB)
results_final-unpol-xs_He-3.txt (2 kB)
results_pol-sf_He-3.txt (1 kB)
results_quark-ratios.txt (1 kB)
syst-err_A1.txt (3 kB)
syst-err_a2.txt (1 kB)
syst-err_d2n.txt (1 kB)
syst-err_final-asym_He-3.txt (2 kB)
syst-err_final-unpol-xs_He-3.txt (1 kB)
syst-err_g1F1.txt (3 kB)
syst-err_pol-sf_He-3.txt (2 kB)
syst-err_quark-ratios.txt (3 kB)