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

TL;DR

This study examines how initial state fluctuations influence elliptic flow in heavy ion collisions using a combined Boltzmann and hydrodynamics approach, finding that final elliptic flow is largely unaffected by these fluctuations in mid-central collisions.

Contribution

It demonstrates that initial state fluctuations have minimal impact on elliptic flow in mid-central collisions and that most flow develops during hydrodynamics, simplifying transport property extraction.

Findings

Elliptic flow is independent of initial fluctuations in mid-central collisions.

Most elliptic flow develops during the hydrodynamic phase.

Using averaged initial conditions does not increase uncertainties in transport property measurements.

Abstract

The effects of initial state fluctuations on elliptic flow are investigated within a (3+1)d Boltzmann + hydrodynamics transport approach. The spatial eccentricity ($\epsilon_{\rm RP}$ and $\epsilon_{\rm part}$) is calculated for initial conditions generated by a hadronic transport approach (UrQMD). 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 build 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.