Jetography in Heavy Ion Collisions

In the last two decades, ultra-relativistic heavy ion colliders have unlocked the study of the Quark Gluon Plasma (QGP) - a hot, dense, and rapidly expanding state of matter exhibiting both deconfinement of its partonic degrees of freedom and signatures of collective behaviour (e.g. nearly zero viscosity). Due to its extremely short lifetime (10^-24 s) the QGP is mainly studied through probes such as jets, clusterings of final state hadrons with a common partonic origin. Since jet development covers a wide range of energies, the modifications of these observables due to the QGP, known as jet quenching, provide valuable insight into QGP development.

Theoretical descriptions of jet quenching still lack a unified framework for both vacuum-like and medium-induced radiation, a task complicated by the former being formulated in momentum space while the latter requires some interface with the coordinate space development of the medium. Since most state-of-the-art models postulate some space-time picture of jet development based on the splitting kinematics, we set out to explore different but equivalent formulations of vacuum-like emissions by building Monte-Carlo Parton Showers ordered in formation time, invariant mass, and opening angle, and considering the impact of these choices on a simplified jet quenching model. We find significant variation between orderings, particularly for thin media.

Another shortcoming lies in the breakdown of colour coherence, which guarantees angular ordering of vacuum-like emissions. While medium-induced emissions are known to violate this condition, current results are limited by reliance on simplified scattering rates, valid only in restricted phase-space regions. Inspired by a previously introduced formalism based on Dyson-Schwinger equations, we compute the decoherence parameter of a quark-antiquark antenna in the QGP for two realistic scattering rates.