Color matrix element corrections for parton showers

TL;DR

This paper explores the impact of including full color structure in parton shower simulations, showing that subleading color corrections are generally small but can be significant for certain observables, especially in soft physics.

Contribution

It introduces a method to incorporate full color matrix element corrections in parton showers within Herwig 7, improving the accuracy of radiation pattern modeling.

Findings

Subleading Nc corrections are small for most hard perturbative observables.

Significant effects (over 10%) are observed in some observables.

Larger effects are found in soft physics regimes.

Abstract

We investigate the effects of keeping the full color structure for parton emissions in parton showers for both LEP and LHC. This is done within the Herwig 7 dipole shower, and includes gluon emission, gluon splitting, initial state branching processes, as well as hadronization. The subleading Nc terms are included as color matrix element corrections to the splitting kernels by evolving an amplitude-level density operator and correcting the radiation pattern for each parton multiplicity, up to a fixed number of full color emissions, after which a standard leading color shower takes over. Our results are compared to data for a wide range of LEP and LHC observables and show that the subleading Nc corrections tend to be small for most observables probing hard, perturbative dynamics, for both LEP and LHC. However, for some of these observables they exceed 10%. On soft physics we find signs of significantly larger effects.