Polarized Nucleon Structure at Large x

The virtual photon asymmetry of the neutron $A_1^n$ is one of the fundamental quantities which provides information about the spin structure of the nucleon. $A_1^n$ at high $x$ is of particular interest because valence quarks dominate in this region, allowing for a cleaner interpretation of experimental results in terms of the nucleon spin structure.  The 6 GeV Jefferson Lab (JLab) results on $A_1^n$ showed that the down quark helicity in the proton ($\Delta d/d$) is negative up to $x\approx 0.61$, in contrast with pQCD predictions that $\Delta d/d$ turns positive and approaches 1 at $x\to 1$.  In this talk I will report on a recently completed precision $A_1^n$ measurement using the 11 GeV beam and an upgraded polarized $^3$He target at Jefferson Lab, that provided data up to $x=0.75$.