A comparison study of medium-modified QCD shower evolution scenarios

TL;DR

This paper compares three models of medium-modified QCD shower evolution in heavy-ion collisions, highlighting their differences through jet observables, and discusses their implications for understanding the medium's microscopic properties.

Contribution

It introduces and compares three different implementations of shower-medium interactions in heavy-ion collisions, exploring their observable differences.

Findings

Single hadron observables like R_AA cannot distinguish models.

Jet observables, such as longitudinal momentum spectra, can differentiate scenarios.

Medium-induced pQCD radiation and drag force models show distinct signatures.

Abstract

The computation of hard processes in hadronic collisions is a major success of perturbative Quantum Chromodynamics (pQCD). In such processes, pQCD not only predicts the hard reaction itself, but also the subsequent evolution in terms of parton branching and radiation, leading to a parton shower and ultimately to an observable jet of hadrons. If the hard process occurs in a heavy-ion collision, a large part of this evolution takes place in the soft medium created along with the hard reaction. An observation of jets in heavy-ion collision thus allows a study of medium-modified QCD shower evolution. In vacuum, Monte-Carlo (MC) simulations are well established tools to describe such showers. For jet studies in heavy-ion collisions, MC models for in-medium showers are currently being developed. However, the shower-medium interaction depends on the nature of the microscopic degrees of freedom of the medium created in a heavy-ion collision which is the very object one would like to investigate. This paper presents a study in comparison between three different possible implementations for the shower-medium interaction, two of them based on medium-induced pQCD radiation, one of them a medium-induced drag force, and shows for which observables differences between the three scenarios become visible. We find that while single hadron observables such as R_AA are incapable of differentiating between the scenarios, jet observables such as the longiudinal momentum spectrum of hadrons in the jet show the potential to do so.