Measurements of $d_2^n$ and $A_1^n$: Probing the neutron spin structure

Journal Article · Tue Sep 06 00:00:00 EDT 2016 · Physical Review D

DOI:https://doi.org/10.1103/PhysRevD.94.052003· OSTI ID:1320788

Flay, D.; Posik, M.; Parno, D. S.; Allada, K.; 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, C.; Fassi, L. El; Franklin, G. B.; Friend, M.; Gao, H.; Garibaldi, F.; Gilad, S.; Gilman, R.; Glamazdin, O.; Golge, S.; Gomez, J.; Guo, L.; Hansen, O.; Higinbotham, D. W.; Holmstrom, T.; Huang, J.; Hyde, C.; Ibrahim, H. F.; Jiang, X.; Jin, G.; Katich, J.; Kelleher, A.; Kolarkar, A.; Korsch, W.; Kumbartzki, G.; LeRose, J. J.; Lindgren, R.; Liyanage, N.; Long, E.; Lukhanin, A.; Mamyan, V.; McNulty, D.; Meziani, Z. -E.; Michaels, R.; Mihovilovič, M.; Moffit, B.; Muangma, N.; Nanda, S.; Narayan, A.; Nelyubin, V.; Norum, B.; Nuruzzaman,; Oh, Y.; Peng, J. C.; Qian, X.; Qiang, Y.; Rakhman, A.; Ransome, R. D.; Riordan, S.; Saha, A.; Sawatzky, B.; Shabestari, M. H.; Shahinyan, A.; Širca, S.; Solvignon, P.; Subedi, R.; Sulkosky, V.; Tobias, W. A.; Troth, W.; Wang, D.; Wang, Y.; Wojtsekhowski, B.; Yan, X.; Yao, H.; Ye, Y.; Ye, Z.; Yuan, L.; Zhan, X.; Zhang, Y.; Zhang, Y. -W.; Zhao, B.; Zheng, X.

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 ($$d_{2}^{n}$$) was conducted. This quantity 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 spin structure functions $$g_1$$ and $$g_2$$ on $$^{3}$$He after nuclear corrections had been applied to these moments. The kinematics included two average $$Q^{2}$$ bins of $3.2$ GeV$$^{2}$$ and $4.3$ GeV$$^{2}$$, and Bjorken-$$x$$ $$0.25 \leq x \leq 0.90$$ covering the DIS and resonance regions. We found $$d_2^n$$ to be small and negative for $ = 3.2$ GeV$$^{2}$$, and smaller for $ = 4.3$ GeV$$^{2}$$, consistent with a lattice QCD calculation. The twist-4 matrix element $$f_{2}^{n}$$ was extracted by combining our $$d_{2}^{n}$$ with the world data on $$\Gamma_{1}^{n} = \int_{0}^{1} g_{1}^{n} dx$$. We found $$f_{2}^{n}$$ to be roughly an order of magnitude larger than $$d_{2}^{n}$$. Utilizing the extracted $$d_{2}^{n}$$ and $$f_{2}^{n}$$ data, we separated the color force into its electric and magnetic components, $$F_{E}^{y,n}$$ and $$F_{B}^{y,n}$$, and found them to be equal and opposite in magnitude, in agreement with instanton model predictions but not with those from QCD sum rules. Additionally, we have extracted the neutron virtual photon-nucleon asymmetry $$A_{1}^{n}$$, the structure function ratio $$g_{1}^{n}/F_{1}^{n}$$, and the quark ratios $$(\Delta u + \Delta \bar{u})/(u + \bar{u})$$ and $$(\Delta d + \Delta \bar{d})/(d + \bar{d})$$. Lastly, these results were found to be consistent with DIS world data and with the prediction of the constituent quark model but at odds with those of perturbative QCD at large $$x$$.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Univ. of Virginia, Charlottesville, VA (United States); Mississippi State Univ., Mississippi State, MS (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• Contributing Organization: Jefferson Lab Hall A Collaboration
• Grant/Contract Number: FG02-94ER40844; FG02-87ER40315; AC05-060R23177; SC0014325; FG02-07ER41528
• OSTI ID: 1320788
• Alternate ID(s): OSTI ID: 1319975; OSTI ID: 1417865
• Report Number(s): JLAB-PHY-16-2297; DOE/OR/23177-3873; arXiv:1603.03612; PRVDAQ
• Journal Information: Physical Review D, Vol. 94, Issue 5; ISSN 2470-0010
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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