Studying the Infrared Behaviour of Improved Logarithmic Accuracy Parton Showers with Herwig

TL;DR

This paper implements and compares two advanced dipole shower algorithms with next-to-leading-logarithmic accuracy in Herwig, analyzing their properties, effects on hadronization, and tunability.

Contribution

It introduces two new dipole shower algorithms with improved logarithmic accuracy and studies their impact on parton shower modeling and hadronization in Herwig.

Findings

The new showers have improved properties in the logarithmic regime.

Infrared cutoff definitions significantly influence hadronization outcomes.

Optimal parameters for each model are identified through tuning.

Abstract

We have implemented two recently proposed dipole shower algorithms that have next-to-leading-logarithmic accuracy at leading colour in the Herwig event generator. We study their properties and compare them to Herwig's existing dipole and angular ordered parton shower algorithms. In addition to their improved properties in the logarithmic regime, we find important roles for their extrapolations into the hard regime, where we perform NLO matching, and into the infrared regime, where we perform cluster hadronization. We emphasise the importance of this infrared regime and the precise definition of the infrared cutoff used by each shower as the initial state for Herwig's hadronization model. Studying the results at the hadron level, we find important consequences of this infrared cutoff difference and propose it as a starting point for further study of the interplay between parton showers and hadronization models. We conclude by studying the models' tunability and identifying the best-fit parameters for each.