Iurii Karpenko

While hybrid approaches of relativistic hydrodynamics + transport have been well established for the dynamical description of heavy-ion collisions at high beam energies, moving to lower beam energies is challenging. In this work, we propose dynamic initial conditions for the viscous hydrodynamic evolution in heavy-ion collisions at low to intermediate beam energies. They are comprised of core hadrons based on the local energy density during the preequilibrium hadronic evolution. The hybrid approach is then applied to lower beam energies, achieving good agreement with measured bulk observables between s N N = 3 and 9.1 GeV , thus providing theoretical guidance for the Beam Energy Scan performed by the STAR Collaboration at RHIC and the future Compressed Baryonic Matter experiment at GSI.

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 report on construction of a modern multi-fluid approach to heavyion collisions at FAIR/BES energies (MUFFIN) and show the reproduction of basic experimental observables in Au-Au collisions in the RHIC Beam Energy Scan program. We also show the p_T-differential and p_T-integrated polarization of (anti-)A hyperons. In MUFFIN simulations, we observe a strong splitting between polarizations of A and anti-A. The splitting is driven purely by a finite baryon chemical potential.

We present directed flow of protons and pions, as well as mean polarization of Λ and ¯Λ hyperons computed for Au-Au collisions at √S_NN = 5 … 19.6 GeV in MUFFIN model. MUlti Fluid simulation for Fast IoN collisions, or MUFFIN, is a state-of-the-art 3-fluid dynamic model for simulating heavy-ion collisions in the region from a few to a hundred GeV center-of-mass energy. Whereas MUFFIN succeeds to reproduce basic observables in the collision energy range of interest, the slope of the directed flow at mid-rapidity is much steeper as compared to the data, it has unclear EoS dependence and final-state hadronic cascade affects this observable significantly. The excitation function of the Λ polarization shows a significant splitting between polarizations of Λ and ¯Λ, which challenges a widespread interpretation that the splitting is affected mainly by the late-stage magnetic field.