Impact of the initial size of spatial fluctuations on the collective flow in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV

TL;DR

This study uses the PHSD transport model to examine how the initial size of spatial fluctuations affects flow observables in Pb-Pb collisions at 2.76 TeV, finding minimal sensitivity due to early phase interaction rates.

Contribution

It demonstrates that the initial size of spatial fluctuations has limited impact on flow coefficients in high-energy Pb-Pb collisions within the PHSD framework.

Findings

Flow coefficients are well described by the model across centralities.

No significant sensitivity of flow to initial spatial fluctuation size.

Early phase interaction rates are too low to influence flow development.

Abstract

The Parton-Hadron-String-Dynamics (PHSD) transport model is used to study the influence of the initial size of spatial fluctuations of the interacting system on flow observables in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV for different centralities. While the flow coefficients $v_2$, $v_3$, $v_4$ and $v_5$ are reasonably described in comparison to the data from the ALICE Collaboration for different centralities within the default setting, no essential sensitivity is found with respect to the initial size of spatial fluctuations even for very central collisions where the flow coefficients are dominated by the size of initial state fluctuations. We attribute this lack of sensitivity partly to the low interaction rate of the degrees-of-freedom in this very early phase of order $\sim$ 0.3 fm/c which is also in common with the weakly interacting color glass condensate (CGC) or glasma approach. Moreover, since the event shape in the transverse plane is approximately the same for different size of spatial fluctuations very similar eccentricities $\epsilon_n$ are transformed to roughly the same flow coefficients $v_n$ in momentum space.