Neutron Spin Structure Measurements in JLab Hall A
Recent progress from Jefferson Lab has significantly improved our understanding of the nucleon spin structure in the high-x region. Results from two experiments in Hall A are presented. The first experiment is a precision measurement of the neutron spin asymmetry, A{sub 1}{sup n}, in the high-x (valence quark) region. The results show for the first time that A{sub 1}{sup n} becomes positive at large x, strongly breaking SU(6) (spin-flavor) symmetry. The data trend is in good agreement with SU(6)-breaking valence quark models and with the fits to the previous world data. Combining the A{sub 1}{sup n} results with the world A{sub 1}{sup n} data, the up and down quark spin distributions in the nucleon were extracted. The results showed that for the proton the valence down quark spin is in the opposite direction from that of the proton, in disagreement with predictions of leading-order perturbative QCD models, which neglect quark orbital angular momentum.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research (ER) (US)
- DOE Contract Number:
- AC05-84ER40150
- OSTI ID:
- 833158
- Report Number(s):
- JLAB-PHY-04-278; DOE/ER/40150-2912; nucl-ex/0409027; TRN: US0406431
- Resource Relation:
- Conference: HiX2004, Marseille, Luminy (FR), 07/26/2004--07/28/2004; Other Information: PBD: 1 Sep 2004
- Country of Publication:
- United States
- Language:
- English
Similar Records
New Results on Nucleon Spin Structure
Highlights and Perspectives of the JLab Spin Physics Program