Non-equilibrium effects and spherocity in relativistic proton-nucleus collisions

We examine nonequilibrium dynamics in proton-nucleus collisions at LHC energy by comparing the Parton-Hadron-String-Dynamics (PHSD) transport approach with the (2+1)dimensional viscous hydrodynamic model VISHNew. The latter is initialized with initial conditions extracted from PHSD. We observe that PHSD exhibits highly inhomogeneous energy density profiles on the transverse plane throughout the evolution, while VISHNew efficiently smooths initial spatial irregularities yet maintains significant inhomogeneity due to the smaller space-time size of the medium produced in small systems compared to heavy-ion reactions. The two approaches present also a very different evolution of the bulk viscous pressure. Furthermore, we analyze transverse spherocity distribution in PHSD and the hybrid approach (VISHNew + hadronic afterburner). We find a shift towards isotropic event configurations in PHSD compared to the result of the hybrid model. This dissimilarity should primarily arise from the different descriptions of the medium within the two frameworks. We support the utility of multi-differential measurements based on multiplicity and spherocity selection for studying final-state observables in relativistic proton-nucleus collisions.

Duke Scholars

Author Steffen A. Bass Physics