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Many hybrid models of heavy ion collisions construct the initial state forhydrodynamics from transport models. Hydrodynamics requires that theenergy-momentum tensor $T^{\mu\nu}$ and four-currents $j^{\mu}$ do not deviateconsiderably from the equilibrium ideal-fluid form, but the ones constructedfrom transport do not necessarily possess this property. In this work weinvestigate the space-time picture of $T^{\mu\nu}$ deviations from equilibriumin Au+Au collisions using a coarse-grained transport approach. The collisionenergy is varied in the range $E_{lab} = 5-160A$ GeV. The sensitivity of$T^{\mu\nu}$ deviations from equilibrium to collision centrality, and otherparameters such as the switching criterion, the amount of statistics used toconstruct the initial state, and the smearing parameter $\sigma$ isinvestigated. For low statistics deviations of $T^{\mu\nu}$ from equilibriumare large and dominated by the effect of finite sampling. For large statisticsthe pressure anisotropy plays the most significant role, while the off-diagonalcomponents of $T^{\mu\nu}$ are small in a large volume during the wholeevolution. For all considered energies and centralities the pressure anisotropyexhibits a similar feature: there is a narrow interval of time, when it rapidlydrops in a considerable volume. This allows us to introduce an "isotropizationtime," which is found to decrease with energy and slightly increase withcentrality. The isotropization times are larger than times typically used forinitializing hydrodynamics.

Deviations of the Energy-Momentum Tensor from Equilibrium in the Initial State for Hydrodynamics from Transport Approaches