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

Abstract

We report on measurements of the neutron spin asymmetries A 1,2n and polarized structure functions g 1,2n at three kinematics in the deep inelastic region, with x=0.33, 0.47, and 0.60 and Q2=2.1, 3.5, and 4.8 (GeV/c) 2, respectively. These measurements were performed using a 5.7 GeV longitudinally polarized electron beam and a polarized 3He target. The results for A1n and g1n 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 A1n 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 A2n and g2n have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment d 2n 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 g1n/F1n values based on the quark-parton model. While results for Δu/u agree well with predictions from various models, results for Δd/d disagree with the leading-order PQCD prediction when hadron helicity conservation is imposed.