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

We report on measurements of the neutron spin asymmetries A1,2ⁿ and polarized structure functions g1,2ⁿ at three kinematics in the deep inelastic region, with $x=0.33$, 0.47, and 0.60 and Q²=2.7, 3.5, and 4.80.3em0ex(GeV∕c)², respectively. These measurements were performed using a 5.70.3em0exGeV 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 d₂ⁿ 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.