Resolving the spacetime structure of jets with medium

TL;DR

This paper develops a versatile parton shower algorithm that explores how different evolution variables affect jet quenching predictions, revealing subtle but measurable impacts on jet observables in heavy-ion collisions.

Contribution

It introduces a general evolution variable framework for parton showers, including virtuality, angle, transverse momentum, and formation time, and studies their effects on jet quenching observables.

Findings

Different evolution variables influence jet mass distributions.

Color coherence effects are significant in dense media.

The choice of evolution variable affects phase space and energy loss modeling.

Abstract

Away from the strictly soft and collinear limit of QCD radiation the choice of evolution scale in a parton shower algorithm is ambiguous and several options have been implemented in existing Monte Carlo event generators for proton-proton collisions. However, the resulting space-time evolution could result in subtle differences depending on the particular choice. In this work we quantify measurable consequences of the choice of the evolution variable and show how the implications of such a choice propagates into jet quenching observables. We develop a parton shower algorithm for a general evolution variable, that includes as special cases the virtuality, angle, transverse momentum and formation time. We study the interplay between the shower history for different evolution variables and the phase space affected by parton energy loss. In particular, we implement effects of jet quenching in the dense limit and highlight the role of color coherence effects. We compare the results of the different ordering variables to existing Monte Carlo shower implementations on the parton level by analyzing primary Lund planes. Finally, we study the sensitivity of quenched jets to the choice of evolution variable by confronting our results for a certain key observable, such as the jet mass.