Initial conditions for heavy ion collisions with QCD kinetic theory
We employ the leading order QCD kinetic theory to describe a consistent matching between the initial stage of a heavy ion collision and the subsequent hydrodynamic evolution. We use the linearized kinetic response functions around the non-equilibirum longitudinally expanding background to map initial energy and momentum perturbations to the energy momentum tensor at hydrodynamic initialization time thydro. We check that hadronic observables then become rather insensitive to the cross-over time between kinetic theory and viscous hydrodynamics. The universal scaling of kinetic response in units of kinetic relaxation time tR ∼ η/(sT ) allows for a straightforward application of kinetic pre-equilibration event-by-event.