The research on saturation/CGC physics is ongoing, with a number of open theoretical and phenomenological questions. Therefore, instead of conclusions, in this chapter we briefly review the phenomenology of saturation/CGC physics and list some important open theoretical problems.

Comparison with experimental data

In this section we will give a brief overview of how high energy QCD theory compares with the current experimental data. The reader may wonder whether such a comparison is possible to fit into one short section; indeed, a comparison of saturation/CGC physics with experiment could be a subject for a separate book. However, a serious quantitative comparison with experiment suffers from two major difficulties. The first is that a welldeveloped theoretical approach exists only for the scattering of a dilute parton system on a dense one; the key examples are DIS on nuclei (eA) and the proton-nucleus (pA) collisions considered earlier. At the same time, much of the data exist either for the scattering of a dense parton system on another dense parton system, as is the case in nucleus–nucleus (AA) collisions, or for the scattering of two dilute systems on each other, like DIS on a proton (ep) or proton-proton (pp) collisions. The theoretical progress in the description of these reactions in the saturation/CGC framework is rather limited, with many open questions and opportunities for further research (see Sec. 8.3 for a brief summary of the existing AA results).