Description

The strong force, described by Quantum Chromodynamics (QCD), is responsible for the composition of nucleons from quarks and gluons, the generation of much of their mass, and (effectively) for the structure of atomic nuclei. It played an important role in the early evolution of the Universe and is crucial for the structure of compact stellar objects such as neutron stars. Understanding the properties of matter interacting primarily through the strong force, such as its equation of state, phase diagram, and transport properties (viscosity, electrical conductivity, etc.) is an active research area today. Collisions of heavy nuclei at relativistic energies are a tool for carrying out these studies in a terrestrial laboratory, as they allow the formation of QCD matter at varying temperatures and densities. Information about matter is derived from particles produced during heavy-ion collisions and measured using particle detectors.

The High Acceptance Di-Electron Spectrometer (HADES), installes at GSI, Darmstadt, Germany, focuses on collision energies of a few GeV per nucleon, corresponding to moderate temperatures and high net baryon densities. In this case, particle pair production from the accumulated energy plays a minor role compared to experiments at higher collision energies. Instead, the dynamics of the system is governed by excitations and decays of baryonic resonances, of which Δ(1232) is the most abundant.

Previously, a new iterative method [1] was developed at HADES to extract the resonance signal with high statistical and systematic precision from a large combinatorial background of uncorrelated pion-proton pairs (signal-to-background ratio of the order of 1%). Applying it to data from Au+Au collisions at (sNN)1/2 = 2.42 GeV [2] allowed a multi-differential analysis (invariant mass, transverse momentum, rapidity of the resonance) revealing patterns that cannot be explained by currently available theoretical models.

The proposed PhD project will be realized in collaboration with the author of the iterative method mentioned above, currently an Associate Professor at the Warsaw University of Technology, Poland. The goal will be to extend and adapt the analysis so that it can be used for data sets collected later by HADES: Ag+Ag at (sNN)1/2 = 2.42 GeV and (sNN)1/2 = 2.55 GeV, and Au+Au at (sNN)1/2 = 2.24 GeV. The interpretation of the results will provide an opportunity to cooperate closely with experts in theoretical physics and to extend the methods for analyzing the results of various dynamical models of heavy-ion collisions.

Participation in the project will also be a chance to join a large and vibrant HADES collaboration and to interact with researchers from several institutions in different European countries.

Skills required

good knowledge of nuclear and particle physics Good programming level (C++) Skills for collaborative work

Bibliography

[1] G. Kornakov and T. Galatyuk, Eur.Phys.J.A 55 (2019) 11, 204
[2] J. Adamczewski-Musch et al. (HADES Collaboration), Phys.Lett.B 819 (2021) 136421

Keywords

data analysis, hadronic matter, baryon resonances, simulations