Evolution variable dependence of jet substructure

TL;DR

This paper investigates how the choice of evolution variable in parton shower algorithms affects jet substructure predictions, revealing differences between angular ordered and transverse momentum ordered showers and their dependence on energy scale.

Contribution

The study introduces an interpolating parton shower generator that varies the evolution variable using a parameter, enabling analysis of its impact on jet substructure predictions.

Findings

Angular ordered showers predict wider jets.

Transverse momentum ordered showers predict narrower jets.

Differences increase at higher jet energies.

Abstract

Studies on jet substructure have evolved significantly in recent years. Jet substructure is essentially determined by QCD radiations and non-perturbative effects. Predictions of jet substructure are usually different among Monte Carlo event generators, and are governed by the parton shower algorithm implemented. For leading logarithmic parton shower, even though one of the core variables is the evolution variable, its choice is not unique. We examine evolution variable dependence of the jet substructure by developing a parton shower generator that interpolates between different evolution variables using a parameter $\alpha$. Jet shape variables and associated jet rates for quark and gluon jets are used to demonstrate the $\alpha$-dependence of the jet substructure. We find angular ordered shower predicts wider jets, while relative transverse momentum ($p_{\bot}$) ordered shower predicts narrower jets. This is qualitatively in agreement with the missing phase space of $p_{\bot}$ ordered showers. Such difference can be reduced by tuning other parameters of the showering algorithm, especially in the low energy region, while the difference tends to increase for high energy jets.