  Hot QCD physics studies the nuclear strong force under extreme temperature
and densities. Experimentally these conditions are achieved via high-energy
collisions of heavy ions at the Relativistic Heavy Ion Collider (RHIC) and the
Large Hadron Collider (LHC). In the past decade, a unique and substantial suite
of data was collected at RHIC and the LHC, probing hydrodynamics at the nucleon
scale, the temperature dependence of the transport properties of quark-gluon
plasma, the phase diagram of nuclear matter, the interaction of quarks and
gluons at different scales and much more. This document, as part of the 2023
nuclear science long range planning process, was written to review the progress
in hot QCD since the 2015 Long Range Plan for Nuclear Science, as well as
highlight the realization of previous recommendations, and present
opportunities for the next decade, building on the accomplishments and
investments made in theoretical developments and the construction of new
detectors. Furthermore, this document provides additional context to support
the recommendations voted on at the Joint Hot and Cold QCD Town Hall Meeting,
which are reported in a separate document.
