Joerg Aichelin

In this study we apply the Remler formalism to charmonium production at Super Proton Synchrotron (SPS) and GSI/Facility for Antiproton and Ion Research (FAIR) energies in order to investigate the effects of baryon-rich matter on charmonium production and dissociation in heavy-ion collisions within the parton-hadron-string dynamics. As a first step the Remler formalism is tested in p + p collisions and then applied to p + A collisions in order to extract the nuclear absorption cross section of charmonium, which is then utilized in heavy-ion collisions. We find that the Remler formalism successfully describes charmonium production in heavy-ion collisions at SPS energies when an in-medium heavy quark potential is implemented, in which J / ψ dissociates near T c . Finally, the same formalism is applied to the low CERN/SPS energy and GSI/FAIR energies, where we estimate charmonium production.

The study of the nuclear equation of state (EoS) is one of the primary goals of experimental and theoretical heavy-ion physics. The comparison of recent high-statistics data from the STAR Collaboration with transport models provides a unique possibility to address this topic in a yet-unexplored energy domain. Employing the microscopic N -body parton-hadron-quantum-molecular dynamics transport approach, which allows us to describe the propagation and interactions of hadronic and partonic degrees of freedom, including cluster and hypernucleus formation and dynamics, we investigate the influence of different EoS on bulk observables, the multiplicity, p T , and rapidity distributions of protons, Λ s and clusters up to A = 4, as well as their influence on the collective flow. We explore three different EoS: two static EoS, dubbed “soft” and “hard,” which differ in the compressibility modulus, as well as a soft momentum-dependent EoS. We find that a soft momentum-dependent EoS reproduces most baryon and cluster observables, including the flow observables, quantitatively; however, hard EoS show a similar trend.

We present a fully covariant transport framework for Molecular Dynamics that enables a consistent description of the evolution of relativistic N-body systems. For the first time, we derive relativistic equations of motion incorporating both scalar and vector interactions within a manifestly covariant formulation. This approach addresses several fundamental issues in relativistic many-body dynamics: the implications of different choices of time-constraints, the emergence of the non-relativistic limit, the frame independence of the system's evolution, and the distinct dynamical roles of scalar and vector potentials. These aspects are investigated in detail for the scattering of two- and four-body systems, offering new insights into the consistency and physical interpretation of relativistic interactions in a covariant setting.

We present a new model for jet quenching in a quark gluon plasma (QGP). The jet energy loss has two steps. The initial jet parton with a high virtuality loses energy by a perturbative vacuum parton shower modified by medium interactions until it becomes on shell. Subsequent energy loss originates from elastic and radiative collisions with the medium constituents. Coherency of the radiative collisions is achieved by starting with virtual gluons that act as field dressing of the initial jet parton. These are formed according to a Gunion-Bertsch seed. The QCD version of the LPM effect is obtained by increasing the phase of the virtual gluons through elastic scatterings with the medium. Above a phase threshold, the virtual gluons will be formed and can produce coherent radiation themselves. The model has been implemented in a Monte Carlo code and is validated by successfully reproducing the BDMPS-Z prediction for the energy spectrum of radiated gluons in a static medium. Results for the more realistic case, in which the assumptions of the BDMPS-Z approach are released, are also shown. We investigate the influence of various parameters on the energy spectrum and the transverse momentum distribution, such as the in-medium quark masses, the energy transfer in the recoil process, and the phase accumulation criteria, especially for low and intermediate energy gluons.

We study the system size dependence of heavy quark (HQ) observables at a center-of-mass energy of s N N = 5.02 TeV to explore whether it can provide further constraints on the physical processes which are involved: energy loss of HQs in the quark gluon plasma (QGP), hadronization, and hadronic rescattering. We use the EPOS4HQ approach to study p − p and 0–10% central O-O, Ar-Ar, Kr-Kr, and Pb-Pb reactions and investigate in detail the momentum change of heavy quarks from creation until their detection as part of a hadron as well as the enhancement of heavy baryon production at low p T . We investigate furthermore the origin and the system size dependence of the azimuthal correlations between the heavy quark Q and the heavy antiquark Q ¯ and how one can bypass the problem that correlations are washed out due to the combinatorial background. We conclude that a systematic study of the system size dependence of the momentum loss allows separating the momentum loss due to the passage through the QGP from the momentum change due to hadronization, and that the Q Q ¯ correlations yield insight into the different pQCD processes in which the heavy quarks are created.

Relativistic heavy-ion collisions produce a hot and dense nuclear matter, through which one can study the phase diagram of QCD. Open and hidden heavy flavors are promising probes to search for the properties of the hot and dense nuclear matter under extreme conditions. We present how the production and interactions of open and hidden heavy flavors in heavy-ion collisions are realized in the Parton-Hadron-String Dynamics, which is a non-equilibrium microscopic transport approach for the description of the dynamics of strongly interacting hadronic and partonic matter.