  Ultrarelativistic heavy ion collisions at the laboratory provide a unique
chance to study quantum chromodynamics (QCD) under extreme temperature
(${\approx}150\,\mathrm{MeV}$) and density
(${\approx}1\,\mathrm{GeV}/\mathrm{fm}^3$) conditions. Over the past decade,
experimental results from LHC have shown further evidence for the formation of
the quark-gluon plasma (QGP), a phase that is thought to permeate the early
Universe and is formed in the high-density neutron-star cores. Various QCD
predictions that model the behavior of the low-$x$ gluon nuclear density, a
poorly explored region, are also tested. Since the photon flux per ion scales
as the square of the emitting electric charge $Z^2$, cross sections of so far
elusive photon-induced processes are extremely enhanced as compared to
nucleon-nucleon collisions. Here, we review recent progress on CMS measurements
of particle production with large transverse momentum or mass, photon-initiated
processes, jet-induced medium response, and heavy quark production. These
high-precision data, along with novel approaches, offer stringent constraints
on initial state, QGP formation and transport parameters, and even
parametrizations beyond the standard model.
