10th Anniversary of Universe: Studying the Strongly Interacting Matter in Nuclear Reactions from Intermediate to Ultra-Relativistic Energies

Dear Colleagues,

A series of discoveries in the last two decades have revealed that, in ultra-relativistic heavy-ion collisions (HIC), the so-called strongly interacting Quark Gluon Plasma (sQGP) is created; it has also been found that this filled the Universe in its first microsecond. At the collision energies of the Large Hadron Collider (LHC) at CERN, as well as at the top energies of the Relativistic Heavy Ion Collider (RHIC) at BNL, the sQGP continuously transitions to form a hadronic matter. At lower beam energies, such as the ones available at the future Facility for Antiproton and Ion Research (FAIR) collider at GSI, a first-order phase transition is expected; however, this has not been confirmed experimentally. A Critical Endpoint (CEP) with a second-order phase transition may be present between the two regions. One important goal of today’s high-energy heavy ion physics is to confirm (or experimentally rule out) the existence of the CEP and, if it exists, to characterize it. At RHIC, a Beam Energy Scan (BES) program has been initiated in order to study this phase diagram, and similar has been established at the CERN Super Proton Synchrotron (SPS). Meanwhile, precision studies of new phenomena have been performed at the LHC, with enlightening discoveries such as collectivity in small systems. This effort is strengthened by the new data being employed in LHC experiments, with upgraded detectors.

Within the beam energy regime available at GSI/FAIR, and even at lower energies at the Facility for Rare Isotope Beams (FRIB), the possibility of producing dense nuclear matter enables researchers to study the properties of matter in neutron stars under laboratory-controlled conditions. Such states of matter are still poorly constrained by terrestrial experiments, and thus it is important to reach a general consensus regarding the isospin asymmetric part of the Equation of State via various investigations. This naturally leads to an intersection between the results extracted from heavy-ion collisions and the ones obtained using satellite measurements of neutron star radii and masses, and those extracted via the detection of the gravitational waves produced by neutron star binary mergers. Signals of possible phase transitions from a hadron phase to a QGP phase in the core of neutron stars may also be observed in the emission of neutrinos by Core Collapse Supernovae. In this respect, the correct interpretation of such observations requires an accurate knowledge of the equation of state below saturation density, making the study of HIC at intermediate energies (available at GSI, FAIR, RIKEN and GANIL) vital for the scientific community.

This Special Issue aims to strengthen the possible synergies between investigations performed at different beam energies, commemorate the discovery of the QGP, and discuss its relevance in particle physics and astrophysics.

Prof. Dr. Máté Csanád
Prof. Dr. Panos Christakoglou
Prof. Dr. Giuseppe Verde
Prof. Dr. You Zhou
Guest Editors

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• quark-gluon plasma
• nuclear interactions
• heavy-ion physics
• strong interaction
• phase diagram