Examination of the directed flow puzzle in heavy-ion collisions

Understand

Recent STAR data for the directed flow of protons, antiprotons, and charged pions obtained within the beam energy scan program are analyzed within the parton-hadron-string-dynamics (PHSD and HSD) transport models and a 3-fluid hydrodynamics (3FD) approach.

• Both versions of the kinetic approach, HSD and PHSD, are used to clarify the role of partonic degrees of freedom.
• The PHSD results, simulating a partonic phase and its coexistence with a hadronic one, are roughly consistent with data.
• The hydrodynamic results are obtained for two equations of state (EoS), a pure hadronic EoS and an EoS with a crossover type transition.