  Collisions between hadronic systems at relativistic energies provide a window
on the small-x gluon distributions of fast moving nuclei. It has been predicted
that gluon saturation effects will manifest themselves as a suppression in the
transverse momentum (pT) distribution at a scale which is connected with the
rapidity of the measured particles. Saturation effects are most evident at
large (pseudo)-rapidity, i.e., at small angles relative to the beam direction.
The dependence of the nuclear modification factor on the number of participants
provides a constraint on the mechanism underlying the high-pT suppression. Here
we present results for the nuclear modification factor Rcp at forward rapidity
as a function of system mass comparing results from CuCu, AuAu and dAu
collsions at 200 GeV/NN.
