Jet momentum balance independent of shear viscosity

TL;DR

This paper argues that jet momentum balance measurements can estimate the energy transferred from parton showers to the medium in heavy-ion collisions independently of shear viscosity details, by linking the observed distributions to the bulk medium.

Contribution

It demonstrates that the Cooper-Frye freezeout distribution related to deposited energy is largely independent of shear viscosity, enabling model-independent energy estimates.

Findings

The momentum distribution of secondary jets reflects the underlying medium's thermal distribution.

Energy transfer estimates are robust against variations in shear viscosity.

The approach provides a new way to quantify parton shower energy deposition.

Abstract

Jet momentum balance measurements, such as those recently performed by the CMS collaboration, provide an opportunity to quantify the energy transferred from a parton shower to the underlying medium in heavy-ion collisions. Specifically, I argue that the Cooper-Frye freezeout distribution associated with the energy and momentum deposited by the parton shower is controlled to a significant extent by the distribution of the underlying bulk matter and independent of the details of how deposited energy is redistributed in the medium, which is largely determined by transport coefficients such as shear viscosity. Thus by matching the distribution of momentum associated with the secondary jet in such measurements to the thermal distribution of the underlying medium, one can obtain a model independent estimate on the amount of parton shower energy deposited.