Jet softening and decollimation in heavy-ion collisions

TL;DR

This study tests and combines models of jet fragmentation in quark-gluon plasma, showing that additional jet decollimation is necessary to match experimental data on dijet asymmetry and decorrelation.

Contribution

The paper develops and tests a combined jet fragmentation model incorporating jet decollimation to better reproduce heavy-ion collision data.

Findings

Modifications of parton splitting alone are insufficient.

Jet decollimation reproduces key experimental features.

Jet substructure analysis suggests observable effects.

Abstract

Two suggested models of jet fragmentation in a quark-gluon plasma have been tested, combined and further developed. This has been done by generating hard processes in proton-proton collisions at $\sqrt{s}=2.76$ GeV in PYTHIA 8 with a modified parton shower algorithm. Subsequently, a jet analysis of the final state hadrons have been performed with the FastJet recombination package. The results have been compared to unmodified jets in proton-proton collisions at the same collision energy, and to experimental data obtained by ATLAS. It has been shown that modifications of the parton splitting kernels alone is an insufficient modification to reproduce experimental data on dijet energy asymmetry and azimuthal decorrelation. Additional jet decollimation qualitatively reproduces the main features of the data provided certain variables are chosen aptly. We also study other jet characteristics with the model, such as the jet substructure, that may be observable experimentally in a near future.