Measurements of dⁿ₂ and Aⁿ₁: Probing the Neutron Spin Structure

Authors

D. Flay, Temple University
M. Posik, Temple University
D. S. Parno, Carnegie Mellon University
Kalyan C. Allada, University of KentuckyFollow
W. R. Armstrong, Temple University
T. Averett, College of William and Mary
F. Benmokhtar, Duquesne University
W. Bertozzi, Massachusetts Institute of Technology
A. Camsonne, Thomas Jefferson National Accelerator Facility
M. Canan, Old Dominion University
G. D. Cates, University of Virginia
C. Chen, Hampton University
J. -P. Chen, Thomas Jefferson National Accelerator Facility
S. Choi, Seoul National University, South Korea
E. Chudakov, Thomas Jefferson National Accelerator Facility
F. Cusanno, INFN, Italy
M. M. Dalton, University of Virginia
W. Deconinck, Massachusetts Institute of Technology
C. W. de Jager, Thomas Jefferson National Accelerator Facility
X. Deng, University of Virginia
A. Deur, Thomas Jefferson National Accelerator Facility
Chiranjib Dutta, University of KentuckyFollow
L. El Fassi, Rutgers University - New Brunswick/Piscataway
G. B. Franklin, Carnegie Mellon University
M. Friend, Carnegie Mellon University
H. Gao, Duke University
F. Garibaldi, INFN, Italy
S. Gilad, Massachusetts Institute of Technology
R. Gilman, Thomas Jefferson National Accelerator Facility
O. Glamazdin, Kharkov Institute of Physics and Technology, Ukraine
Ameya Suresh Kolarkar, University of KentuckyFollow
Wolfgang Korsch, University of KentuckyFollow

Abstract

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, 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 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.

Document Type

Article

Publication Date

9-6-2016

Notes/Citation Information

Published in Physical Review D, v. 94, issue 5, 052003, p. 1-51.

© 2016 American Physical Society

The copyright holder has granted permission for posting the article here.

Due to the large number of authors, only the first 30 and the authors affiliated with the University of Kentucky are listed in the author section above. For the complete list of authors, please download this article.

The authors of this article are collectively known as Jefferson Lab Hall A Collaboration.

Digital Object Identifier (DOI)

https://doi.org/10.1103/PhysRevD.94.052003

Funding Information

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.

Related Content

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.

Repository Citation

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.
https://uknowledge.uky.edu/physastron_facpub/433