Der Hadronisierungsprozess in relativistischen Kernkollisionen und das Phasendiagramm der QCD

• Antragsteller: Professor Dr. Reinhard Stock
• Fachliche Zuordnung: Kern- und Elementarteilchenphysik, Quantenmechanik, Relativitätstheorie, Felder
• Förderung: Förderung von 2013 bis 2019
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 226167684

Collisions of heavy nuclei at relativistic energies create a "fireball" volume of strongly interacting matter, at an energy density that increases with collision energy. At a certain "critical" energy density the initial hadronic confinement of partons is overcome, giving rise to the formation of a state with mobile partons: the so-called "Quark-Gluon Plasma" predicted by non-perturbative Quantum Chromodynamics (QCD). Its domain of existence, and detailed properties represent a sector of strong interaction theory that is not well settled: the subject also of accompanying experimental studies of relativistic A+A collisions. At high collision energy the plasma fireball emits all known hadrons, leptons and resonances of the Standard Model. Experiments specializing on measurement of the final hadron/resonance composition, in conjunction with the statistical hadronization model introduced by R. Hagedorn, derive a tentative hadronization point in the plane of temperature vs. baryochemical potential (essentially net baryon density), at each incident energy considered. This plane is also commonly employed to represent the "phase diagram of QCD matter". Entries from recent non-perturbative QCD concern, primarily, the position and nature of the parton-hadron coexistence line in (T,mu(B)). It may feature a critical point of QCD, as well as branches separating further hypothetical states of QCD matter. Such predictions are confronted, for example, with the semi-empirical hadron formation (or "freeze-out") data, that constitute a "hadronic freeze-out curve" in the (T,mu(B)) plane. The relation of this curve to the theoretically conjectured phase coexistence line is the subject of the study proposed here. As members of the experiment STAR at the RHIC collider we shall gather new, high statistics data from the current RHIC low energy runs. In conjunction with data that we obtained previously at the CERN SPS in our experiment NA49, we will attempt a new determination of the hadronic freeze-out line, in the intermediate energy domain corresponding to the interval 200 < mu(B) < 450 MeV. Looking, specifically, for substantiation of its well-know but not understood deviation from the lattice-QCD parton-hadron phase boundary line, occurring in this domain. This finding, if confirmed, invites speculations concerning an intervening, further state of QCD matter ("Quarkyonic Matter"). And for indication of a nonmonotonic behavior of the freeze-out curve that could be attributed to effects of the critical point (due to refocusing of the expansion trajectory in (T,mu(B))). We shall confront the data with the statistical hadronization model, and with the microscopic transport model (UrQMD), in this study.

• DFG-Verfahren: Sachbeihilfen