Analysis of Ultra-Central Relativistic Heavy Ions Collisions Based on Energy Parameterization

Hydrodynamic models of heavy-ion collisions have been very successful at describing experimental data. A peculiar exception is anisotropic flow in ultra-central collisions. No existing model for the initial stages of a heavy-ion collision, when used as initial conditions for hydrodynamics simulations, can provide a satisfactory description of flow in ultra-central collisions. It is therefore useful to understand what properties the initial stages must have in order to be compatible with experimental data. To this end, we parameterize the early-time energy density and its fluctuations via its 1-point and 2-point function and constrain them by using experimental data for vn2 in conjunction with hydrodynamic simulations. We find that it is possible to describe experimental data, but it requires larger fluctuations in regions of low density, as compared to existing Monte Carlo models. We comment on the implications of this finding, as well as the limitations of this initial analysis and how it can be improved in the future.