How High is High x?

Abstract

A general three quark bound state satisfying the Pauli principle, and conserving angular momentum and isospin, is used to investigate the spin structure of nucleons at high $x$. It is shown that, if a spin up quark dominates as $x$$\to$1 for a spin up proton, it must be a u quark. Then both $A_{1p}$ and $A_{1n}$, as well as the quark spin distribution $\Delta u/u$, will approach 1 as $x$$\to$1. The spin distribution $\Delta d/d$ does not approach 1, but is bound by the limits $-{1/3}\le\Delta d/d\le 0$ for any $x$. The ratio {$F_{1n}/F_{1p}$ will approach 1/4} (not3/7).