Pre-hydrodynamic evolution and its impact on quark-gluon plasma signatures

Abstract

State-of-the-art hydrodynamic models of heavy-ion collisions have considerable theoretical model uncertainties in the description of the very early pre-hydrodynamic stage. We add a new computational module, K${}_{\mathrm{T}}$Iso, that describes the pre-hydrodynamic evolution kinetically, based on the relativistic Boltzmann equation with collisions treated in the Isotropization Time Approximation. As a novelty, K${}_{\mathrm{T}}$Iso allows for the inclusion and evolution of initial-state momentum anisotropies. To maintain computational efficiency K${}_{\mathrm{T}}$Iso assumes strict longitudinal boost invariance and allows collisions to isotropize only the transverse momenta. We use it to explore the sensitivity of hadronic observables measured in relativistic heavy-ion collisions to initial-state momentum anisotropies and microscopic scattering during the pre-hydrodynamic stage.