A case study of quark-gluon discrimination at NNLL' in comparison to parton showers

TL;DR

This study compares analytic resummed predictions for quark-gluon discrimination at NNLL' with parton shower models, highlighting improved agreement with recent Herwig 7.1 results and analyzing uncertainties from hadronization and perturbative effects.

Contribution

It provides a detailed comparison between NNLL' resummed predictions and parton shower models, emphasizing the impact of recent Herwig updates on gluon jet modeling.

Findings

Reasonable agreement between NNLL' predictions and parton showers.

Improved gluon jet description in Herwig 7.1.

Uncertainty estimates include hadronization and perturbative effects.

Abstract

Predictions for our ability to distinguish quark and gluon jets vary by more than a factor of two between different parton showers. We study this problem using analytic resummed predictions for the thrust event shape up to NNLL' using $e^+e^- \to Z \to q \bar q$ and $e^+e^- \to H \to gg$ as proxies for quark and gluon jets. We account for hadronization effects through a nonperturbative shape function, and include an estimate of both perturbative and hadronization uncertainties. In contrast to previous studies, we find reasonable agreement between our results and predictions from both Pythia and Herwig parton showers. We find that this is due to a noticeable improvement in the description of gluon jets in the newest Herwig 7.1 compared to previous versions.