  In order to understand the initial partonic state in proton-nucleus and
electron-nucleus collisions, we investigate the total, inelastic, and
(quasi-)elastic cross sections in pA and gamma-A collisions, as these
observables are insensitive to possible collective effects in the final state
interactions. We used as a tool the DIPSY dipole model, which is based on BFKL
dynamics including non-leading effects, saturation, and colour interference,
which we have extended to describe collisions of protons and virtual photons
with nuclei. We present results for collisions with O, Cu, and Pb nuclei, and
reproduce preliminary data on the pPb inelastic cross section at LHC by CMS and
LHCb. The large NN cross section results in pA scattering that scales
approximately with the area. The results are compared with conventional Glauber
model calculations, and we note that the more subtle dynamical effects are more
easily studied in the ratios between the total, inelastic and (quasi-)elastic
cross sections. The smaller photon interaction makes the gamma-A collisions
more closely proportional to A, and we see here that future electron-ion
colliders would be valuable complements to the pA collisions in studies of
dynamical effects from correlations, coherence and fluctuations in the initial
state in high energy nuclear collisions.
