A bstract 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 p A and γ _(?) 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 p A 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 γ _(?) A collisions more closely proportional to A , and we see here that future electron-ion colliders would be valuable complements to the p A collisions in studies of dynamical effects from correlations, coherence and fluctuations in the initial state in high energy nuclear collisions.
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