This program studies the nature of strongly interacting matter and exploration of the QCD phase diagram. Lattice QCD calculations indicate that at sufficiently high temperatures (~2 trillion degrees), nuclear matter dissolves into a plasma of quarks and gluons, called the quark-gluon plasma (QGP). The QGP filled the universe 10 microseconds after the Big Bang, and may exist today in the cores of neutron stars.

On Earth, the QGP can only be studied via the collision of heavy atomic nuclear at very high energy, and we perform such studies as members of the STAR and sPHENIX experiments at the Relativistic Heavy Ion Collider (RHIC) at BNL, and the ALICE experiment at the Large Hadron Collider (LHC) at CERN. The picture of the QGP that has emerged from these experimental studies is quite different from initial theoretical expectations of a rather featureless gas of non-interacting quarks and gluons. Rather, the QGP displays complex and fascinating collective behavior, whose basic constituents are “quasi-particles” that are quite different from bare quarks and gluons, and appear to interact with the lowest viscosity allowed by nature. Experimental study of the QGP has attracted attention from neighboring fields of physics, including condensed matter, plasma physics, and even string theory.

The RNC has played a central role in the STAR experiment throughout its history, leading fundamental discoveries about the QGP. Most significantly, the collective dynamical behavior of the QGP and the interaction and modification of hard QCD jets in the QGP, or “jet quenching”, as predicted by our theory colleagues in the NSD. More recently, members of the RNC group have turned their attention to questions about the behavior of heavy quarks in the QGP, as well as to an experimental search for the QGP critical point via a beam energy scan (BES). The RNC recently joined the new sPHENIX experiment in pursuit of next-generation heavy quark measurements needed to characterize the microscopic picture of the QGP.

The RNC also plays a key role in A Large Ion Collider Experiment (ALICE) at the LHC. The main aim of ALICE is to characterize the physical properties of the QGP created with heavy ion collisions at the LHC but to also study QCD in smaller systems such as proton-proton, proton-lead, Oxygen-Oxygen and possibly more-to-come (e.g. Argon-Argon) in future LHC runs. RNC scientists working within ALICE Collaboration are focused on two directions: 1) unraveling the microscopic picture of jet quenching within QGP using jets and heavy quarks and 2) ultra-peripheral collisions (UPCs) allowing to study structure of nuclei and properties of hadrons. Performing experiments at the LHC is an ideal opportunity for detailed studies using these rare probes thanks to the high energy (currently highest achieved in a laboratory) of the collisions between ions or other species achieved at CERN. LHC’s Run 3 began in 2022 and members of the RNC play an active role in the collection and analysis of the new, high precision, data that ultimately will allow us to perform state-of-the-art measurements providing new, otherwise unreachable, insights into the properties of QGP.