Understanding the properties of extremely dense nuclear matter is an important part of theoretical and experimental studies of Quantum Chromodynamics (QCD), the quantum field theory describing the strong interactions between quarks and gluons (partons). At high energies, the parton densities in nuclei are expected to become so large that emergent so called saturation effects start to strongly contribute to the partonic structure of protons and nuclei and limit how large densities can be achieved in nature. Revealing the properties of this new state of matter is fundamentally intriguing in itself. It is also important from the heavy ion physics point of view, as a detailed description of the initial states of the colliding nuclei is a necessary input for the extraction of the fundamental properties of Quark Gluon Plasma produced in heavy ion collisions at high energies.
There are solid theoretical arguments suggesting the existence of gluon saturation. However, no solid experimental signatures of this phenomenon have been observed so far. In order to probe QCD dynamics in the high-density region where saturation effects should be visible, new theoretical and experimental developments are necessary. On the experimental side, high-energy collisions with heavy nuclei at the LHC will be complemented by electron-nucleus collisions performed for the first time at the Electron-Ion Collider, that will start to collect data in the US within the next decade. On the theoretical side, it is crucial to develop precision level calculations describing the physics of gluon saturation to the level where global analyses taking advantage of the complementarity between the LHC and the future EIC measurements are possible. This is exactly what we plan to do in the new ERC CoG project ”Shining light on saturated gluons” presented in this talk.
