The contribution of hard processes to elliptic flow

TL;DR

This paper investigates how momentum transfer from numerous hard partons can influence the elliptic flow in heavy-ion collisions, potentially affecting interpretations of early thermalization and viscosity.

Contribution

It introduces the idea that diffusion wakes from hard partons may contribute to azimuthal asymmetry in elliptic flow, a factor often neglected in analyses.

Findings

Hard partons induce diffusion wakes affecting flow.

Small but non-negligible contribution to azimuthal asymmetry.

Implications for interpreting v2 measurements in heavy-ion collisions.

Abstract

I study a possible effect of momentum deposition from many hard partons traversing the hot and dense region produced early in nuclear collisions at the LHC. The expected number of such hard partons is large. It is argued that the induced diffusion wakes which carry the momentum deposited to the medium may interact. Due to azimuthally asymmetric geometry in non-central collisions, this may lead to small preference of the collective flow in the direction of the impact parameter. As a result, a small contribution to the azimuthal asymmetry of hadronic spectra is obtained. It may be important to take even such a small contribution into account if quantitative conclusions about early thermalisation and low viscosity are to be made, based on the measurements of the elliptic flow parameter v2.