Mapping the hydrodynamic response to the initial geometry in heavy-ion collisions

Abstract

We investigate how the initial geometry of a heavy-ion collision is transformed into final flow observables by solving event-by-event ideal hydrodynamics with realistic fluctuating initial conditions. We study quantitatively to what extent anisotropic flow (v n ) is determined by the initial eccentricity ε n for a set of realistic simulations, and we discuss which definition of ε n gives the best estimator of v n . We find that the common practice of using an r 2 weight in the definition of ε n in general results in a poorer predictor of v n than when using r n weight, for n > 2. We similarly study the importance of additional properties of the initial state. For example, we show that in order to correctly predict v 4 and v 5 for noncentral collisions, one must take into account nonlinear terms proportional to ε 2 2 and ε 2 ε 3 , respectively. We find that it makes no difference whether one calculates the eccentricities over a range of rapidity or in a single slice at z = 0, nor is it important whether one uses an energy or entropy density weight. This knowledge will be important for making a more direct link between experimental observables and hydrodynamic initial conditions, the latter being poorly constrained at present.

Anisotropic Flow in Event-by-Event Ideal Hydrodynamic Simulations ofsNN=200 GeVAuGardim1, Grassi2, Luzum3 et al. 2012Phys. Rev. Lett.Self Cite

“…(2), with the average taken over all particles in the pseudorapidity interval −1 < η < 1. The procedure used to measure v n in hydrodynamics thus mimics the experimental procedure, with two differences: (i) there is no need for a rapidity gap, because nonflow correlations are negligible; (ii) there is no need for a resolution correction, because the huge multiplicity per event ensures that the resolution is close to 1 for all events [47]. Fig.…”

“…As in Ref. [47], at the end of each hydro event, we run the Monte-Carlo generator many times, so that we can do the flow analysis using approximately 6 × 10 5 particles per event. This significantly reduces statistical noise and allows for an accurate determination of v n and Ψ n in every event.…”

Event-by-EventHydrodynamics+JetEnergy Loss: A Solution to theRAA⊗vNoronha-Hostler1, Betz2, Noronha3 et al. 2016Phys. Rev. Lett.11861573View full textAdd to dashboardCite

“…We found that hcos [2 2 ]i ⇠ 0.99 while hcos [3 3 ]i ⇠ 0.33 in our simulation. It would be interesting to test if there is an analog of the mapping of the eccentricities onto the final high p T flow harmonics that also mirrors the soft correlation seen at low p T [97][98][99].…”

An estimate of the bulk viscosity of the hadronic medium

“…The effects of these transport coefficients on the hydrodynamic evolution of the strongly interacting fireball and on various observables in HICRE, e.g. the elliptic flow, spectra of hadronic and electromagnetically interacting particles, etc have been studied extensively [3][4][5][6][7][8]. The general consensus reached is that the matter created in heavy ion collisions behaves almost like a perfect liquid [9][10][11][12][13] with η/s close to the KSS (Kovtun, Son and Starinets) bound [14].…”