Precision measurement of the neutron spin asymmetries and spin-dependent structure functions in the valence quark region

Journal Article · Tue Nov 30 23:00:00 EST 2004 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PhysRevC.70.065207· OSTI ID:20695845

Zheng, X; Bertozzi, W; Chai, Z; Dutta, D; Gao, H; Gilad, S; Higinbotham, D W; Rvachev, M; Sirca, S; Xiang, H; Xiao, Y; Xiong, F; Zhang, B; Zhu, L ^[1]; Aniol, K; Margaziotis, D J ^[2]; Armstrong, D S; Butuceanu, C; Finn, J M; Kramer, K ^[3]

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1. Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
2. California State University, Los Angeles, Los Angeles, California 90032 (United States)
3. College of William and Mary, Williamsburg, Virginia 23187 (United States); and others

We report on measurements of the neutron spin asymmetries A{sub 1,2}{sup n} and polarized structure functions g{sub 1,2}{sup n} at three kinematics in the deep inelastic region, with x=0.33, 0.47, and 0.60 and Q{sup 2}=2.7, 3.5, and 4.8 (GeV/c){sup 2}, respectively. These measurements were performed using a 5.7 GeV longitudinally polarized electron beam and a polarized {sup 3}He target. The results for A{sub 1}{sup n} and g{sub 1}{sup n} at x=0.33 are consistent with previous world data and, at the two higher-x points, have improved the precision of the world data by about an order of magnitude. The new A{sub 1}{sup n} data show a zero crossing around x=0.47 and the value at x=0.60 is significantly positive. These results agree with a next-to-leading-order QCD analysis of previous world data. The trend of data at high x agrees with constituent quark model predictions but disagrees with that from leading-order perturbative QCD (PQCD) assuming hadron helicity conservation. Results for A{sub 2}{sup n} and g{sub 2}{sup n} have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment d{sub 2}{sup n} was evaluated and the new result has improved the precision of this quantity by about a factor of 2. When combined with the world proton data, polarized quark distribution functions were extracted from the new g{sub 1}{sup n}/F{sub 1}{sup n} values based on the quark-parton model. While results for {delta}u/u agree well with predictions from various models, results for {delta}d/d disagree with the leading-order PQCD prediction when hadron helicity conservation is imposed.

• OSTI ID: 20695845
• Journal Information: Physical Review. C, Nuclear Physics, Journal Name: Physical Review. C, Nuclear Physics Journal Issue: 6 Vol. 70; ISSN 0556-2813; ISSN PRVCAN
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ASYMMETRY
DEEP INELASTIC SCATTERING
DISTRIBUTION FUNCTIONS
ELECTRON BEAMS
ELECTRON REACTIONS
ELECTRON-NUCLEON INTERACTIONS
GEV RANGE
HELICITY
HELIUM 3 TARGET
NEUTRONS
PARTON MODEL
PERTURBATION THEORY
POLARIZED BEAMS
POLARIZED TARGETS
PROTONS
QUANTUM CHROMODYNAMICS
QUARK MODEL
QUARKS
SPIN
STRUCTURE FUNCTIONS