  High-energy heavy-ion collisions provide a unique opportunity to study the
properties of the hot and dense strongly-interacting system composed of
deconfined quarks and gluons -- the quark-gluon plasma (QGP) -- in laboratory
conditions. The formation of a QGP is predicted by lattice QCD calculations as
a crossover transition from hadronic matter (at zero baryochemical potential)
and is expected to take place once the system temperature reaches values above
155 MeV and/or the energy density above $0.5~\mathrm{GeV}/\mathrm{fm}^{3}$. The
nature of such a strongly coupled QGP has been linked to the early Universe at
some microseconds after the Big Bang. To characterize the physical properties
of the short-lived matter (lifetime of about $10~\mathrm{fm}/c$) experimental
studies at Relativistic Heavy-Ion Collider and the Large Hadron collider use
auto-generated probes, such as high-energy partons created early in the
hadronic collisions, thermally emitted photons, and a set of particle
correlations that are sensitive to the collective expansion and the dynamics of
the system. The lectures briefly introduced some of the experimental techniques
and provided a glimpse at some of the results.
