Neutron Spin Structure Measurements in JLab Hall A
- Jefferson Lab, Newport News, Virginia 23606 (United States)
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 p} data, the up and down quark spins 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.In the second experiment, the Q2 dependence of the moments and sum rules of the spin structure in the low to intermediate Q2 region were measured, providing a unique bridge linking the quark-gluon picture of the nucleon and the coherent hadronic picture.
- OSTI ID:
- 20630639
- Journal Information:
- AIP Conference Proceedings, Vol. 747, Issue 1; Conference: HiX2004: 2. international workshop on the structure of the nucleon at large Bjorken x, Marseille (France), 26-28 Jul 2004; Other Information: DOI: 10.1063/1.1871643; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); JLab Hall A Collaboration; E94-010 Collaboration; ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACCURACY
ASYMMETRY
CEBAF ACCELERATOR
D QUARKS
DISTRIBUTION
FLAVOR MODEL
FOUR MOMENTUM TRANSFER
GLUONS
NEUTRONS
ORBITAL ANGULAR MOMENTUM
PARTICLE KINEMATICS
PROTONS
QUANTUM CHROMODYNAMICS
QUARK-GLUON INTERACTIONS
SPIN
SU-6 GROUPS
SUM RULES
SYMMETRY BREAKING