What have we learned from heavy-ion collisions about the Quark Gluon Plasma?
Under normal conditions of our world, the fundamental particles of the strong interaction, quarks and gluons, are confined in protons and neutrons inside nuclei. However, numerical calculations approximating Quantum Chromo Dynamics (QCD), the theory of the strong interaction, predict at high temperature a state of matter where quarks and gluons are effectively free to move over larger distance, the Quark-Gluon Plasma (QGP).
The goal of high-energy collisions of heavy nuclei is to create the QGP and to study its properties in the laboratory. I will present recent results from heavy ion collisions focusing mainly on data from ALICE at the LHC and discuss what they tell us about the QGP. I will end by giving a brief outlook of future work at the LHC including an upgrade of ALICE for LHC run-4, based on a new technology forward electromagnetic calorimeter to explore the partonic structure of nuclei in an uncharted regime.