Hot and dense QCD matter and heavy-ion collisions

Abstract

Within the standard model of particle physics, strong interactions are responsible for generating the major part of the visible mass in the universe and for confining quarks into hadrons (the building blocks of atomic nuclei). The underlying theory, quantum chromodynamics, is well-established in elementary reactions at high-momentum transfer, but its increasing interaction strength toward smaller momenta renders the understanding of strongly-interacting matter and its phase structure rather challenging. These are relevant to the early universe a few microseconds after the big bang where hadrons were dissolved into a plasma of quarks and gluons. High-energy collisions of heavy nuclei are the only way to recreate this matter in the laboratory. We highlight recent progress in the theoretical understanding of QCD matter in the context of experimental findings at the relativistic heavy-ion collider (RHIC, BNL) and the super-proton synchrotron (SPS, CERN), in particular the properties of heavy quarks (charm and bottom) in the Quark-gluon plasma, and in-medium modifications of the ρ-meson.