Subleading Nc improved Parton Showers

TL;DR

This work introduces color matrix element corrections to a dipole-type parton shower to incorporate full SU(3) color correlations beyond the leading $N_c$ approximation. Emissions are weighted using color-space amplitudes and a matrix evolution $M_n \to M_{n+1}$, with a color-aware sampling algorithm that allows all parton pairs to radiate. In a proof-of-concept for $e^+e^-\to$ jets, standard LEP-like observables show only a few percent changes, whereas tailored observables such as average transverse momentum with respect to a thrust axis exhibit much larger effects (up to ~20%), indicating potential significance for color-coherence studies and high-multiplicity final states. The study demonstrates the feasibility of SU(3)-level showering and outlines future extensions (running coupling, $g\to q\bar q$, virtual color exchanges, hadronization) necessary for a fully realistic, color-correlated event generator.

Abstract

We describe an algorithm for improving subsequent parton shower emissions by full SU(3) color correlations in the framework of a dipole-type shower. As a proof of concept, we present results from the first implementation of such an algorithm for a final state shower. The corrections are found to be small for event shapes and jet rates but can be more significant for tailored observables.