Abstract:
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 $^3$He 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 two. 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 $\Delta
u/u$ 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.