In ultrarelativistic collisions of heavy nuclei, such as those which take place in the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC), the resulting state of matter attains such high temperatures and energy densities that quarks and gluons are no longer confined into hadrons. Known as the quark-gluon plasma (QGP), this matter occupies the high-temperature and high-density regime of the phase diagram of quantum chromodynamics (QCD). By probing the properties of the QGP, we are able to study QCD and the phase diagram of nuclear matter in the extreme high temperature limit.
In this talk, a selection of key measurements will be presented which give insight into the space-time evolution of the QGP and its thermodynamical and hadrochemical properties. In particular, I will discuss how the fluctuations of conserved charges - such as electric charge, strangeness, and baryon number - provide insight into the properties of the matter created in heavy-ion collisions and the phase transition from a QGP phase into a hadron gas. These fluctuations can be related to experimental measurements of the higher moments of the multiplicity distributions of identified particles such as pions, kaons, and protons, and lambda baryons. In this talk, the latest state-of-the-art measurements from ALICE at the LHC and STAR at RHIC will be presented, as well as our current understanding of the challenges inherent in making a connection between measurements and theoretical QCD calculations. Finally, I will close with an outlook towards future measurements in the RHIC Beam Energy Scan Phase II and Runs 3 and 4 at the LHC.