Precision measurement of the neutron spin asymmetries and spin-dependent structure functions in the valence quark region -: art. no. 065207

We report on measurements of the neutron spin asymmetries A(1,2)(n) and polarized structure functions g(1,2)(n) at three kinematics in the deep inelastic region, with x=0.33, 0.47, and 0.60 and Q(2)=2.7, 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 He-3 target. The results for A(1)(n) and g(1)(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(1)(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(2)(n) and g(2)(n) have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment d(2)(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(1)(n)/F-1(n) values based on the quark-parton model. While results for Deltau/u agree well with predictions from various models, results for Deltad/d disagree with the leading-order PQCD prediction when hadron helicity conservation is imposed.