Flow anisotropy due to momentum deposition in ultra-relativistic nuclear collisions

Boris Tomášik,Martin Schulc

doi:10.1051/epjconf/201713713019

Abstract

Minijets and jets are produced in large numbers in nuclear collisions at TeV energies, so that there are many of them in a single fireball. They deposit non-negligible amount of momentum and energy into the hydrodynamically expanding bulk and cause anisotropies of the expansion. Moreover, due to their multiple production in a single event the resulting anisotropies are correlated with the collision geometry and thus contribute positively also to event-averaged anisotropies in non-central collisions. Using simulations with three-dimensional ideal hydrodynamic model we demonstrate the importance of this effect. It must be taken into account if conclusions about the properties of the hot matter are to be drawn.

Highlights

One of the features of heavy-ion collisions at the LHC is the large portion of energy spent in production of hard partons
We can expect more streams within the expanding plasma. If their number is not too large, we can expect an increase of flow anisotropies of all orders. We argue that this contribution to elliptic flow anisotropy is correlated with the geometry of the collision so that it increases the elliptic flow in non-central collisions
The data are compatible with the hypothesis that momentum deposition from jets into plasma and the merging of streams lead to correlated ψ2 and ψ3, while such correlation is absent with the flow anisotropies caused only by initial conditions

Summary

Introduction

One of the features of heavy-ion collisions at the LHC is the large portion of energy spent in production of hard partons. Some of them appear as jets, but a major part of hard and semi-hard partons never comes out of the fireball. Instead, they are fully stopped in the quark-gluon plasma. One would naively expect that they would suppress the flow anisotropy. As it is sketched, in this case the inward-flying jets are more likely to meet. The resulting effect of the pair of dijets on the collective flow would be smaller than in the previous case, since a pair of dijets flying in the direction of the reaction plane is less likely to meet. We shall show that the effect of the jets on flow anisotropies is significant

The model

Results for non-central collisions

Results for central collisions

Conclusions