Eccentricity fluctuations in an integrated hybrid approach: Influence on elliptic flow

The effects of initial state fluctuations on elliptic flow are investigated within a (3 + 1)-dimensional Boltzmann + hydrodynamics transport approach. The spatial eccentricity (epsilon(RP) and epsilon(part)) is calculated for initial conditions generated by a hadronic transport approach (ultrarelativistic quantum molecular dynamics). Elliptic flow results as a function of impact parameter, beam energy, and transverse momentum for two different equations of state and for averaged initial conditions or a full event-by-event setup are presented. These investigations allow the conclusion that in mid-central (b = 5-9 fm) heavy-ion collisions the final elliptic flow is independent of the initial state fluctuations and the equation of state. Furthermore, it is demonstrated that most of the v(2) is built up during the hydrodynamic stage of the evolution. Therefore, the use of averaged initial profiles does not contribute to the uncertainties of the extraction of transport properties of hot and dense QCD matter based on viscous hydrodynamic calculations.