Parton densities and dipole cross-sections at small x in large nuclei

Abstract

Unintegrated gluon densities in nuclei, dipole-nucleus cross-sections and quark densities are numerically investigated in the high-colour limit, with the scattering on a heavy nucleus exactly described by the sum of fan diagrams of BFKL pomerons. The initial condition for the evolution in rapidity is quickly forgotten, and the gluon density presents a "supersaturation" pattern, as previous studies indicated. Both dipole-nucleus cross-sections and quark densities present the expected saturation features. Identifying the position in transverse momentum $l$ of the maximum of the gluon distribution with the saturation momentum $Q_s(y,b)$, at large rapidities all distributions depend only on one variable $[l/Q_s(y,b)]$ or $[r{Q}_s(y,b)]$.

Comments: LaTeX, 13 pages, 6 figures in encapsulated postscript included using epsfig; final version, with two added references plus comments, some further clarification, results and conclusions unchanged