  We argue that the amount of baryon stopping observed in the central rapidity
region of heavy ion collisions at RHIC is proportional to the nuclear valence
quark distributions at small x. By generalizing Mueller's dipole model to
describe Reggeons we construct a non-linear evolution equation for the valence
quark distributions at small x in the leading double-logarithmic approximation.
The equation includes the effects of gluon saturation in it. The solution of
the evolution equation gives a valence quark distribution function $dn_{val}/dy
\sim e^{-(0.4\div0.5) y}$. We show that this y-dependence as well as the
predictions of Regge theory are consistent with the net-proton rapidity
distribution reported by BRAHMS.
