Quark-gluon plasma properties

Abstract

Heavy ion collisions are used to study fundamental features of quantum chromodynamics (QCD) matter via its excitation to phases where quarks and gluons are no more confined into hadrons. Studies of the properties of this deconfined quark–gluon matter, called quark–gluon plasma (QGP), at the Brookhaven Relativistic Heavy-Ion Collider and the LHC have shown that the QGP behaves like a liquid with very small specific shear and bulk viscosities, and high opacity for energetic jets. Macroscopic (microscopic) properties are encoded in the collective expansion (underlying parton dynamics) of the strongly interacting QGP. Here, we review recent progress on measurements at the LHC particle production from small to large transverse momentum or mass, jet-induced medium response, heavy quark and exotic meson production, and photon-initiated processes. Increasingly 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.