Parton Distributions, d/u, and Higher Twists at High X

A re-analysis of data from NMC and SLAC leads to a great improvement in our knowledge of the valence $d$ and $u$ parton distribution functions at high $x$. Standard parton distributions with our modifications are in good agreement with QCD predictions for $d/u$ at $x=1$, and with the CDHSW $\nu p$ and $\bar{\nu} p$ data, the HERA charged current cross section data, the collider high-$P_t$ jet data, and the CDF $W$ asymmetry data. With the inclusion of target mass and higher twist corrections, the modified PDF's also describe all DIS data up to $x = 0.98$ and down to $Q^2 = 1 GeV^2$.