Soft evolution of multi-jet final states

TL;DR

This paper introduces a new framework for resumming and matching multi-jet QCD processes, automating color evolution calculations at next-to-leading-logarithmic accuracy, and implementing these in the Sherpa event generator.

Contribution

It provides an automated method for color evolution in soft gluon emissions and a new tree-level matching scheme for complex multi-jet processes.

Findings

Explicit results for processes with up to 2→5 partons

Implementation of resummation and matching in Sherpa

Resummed and matched transverse-thrust distribution computed

Abstract

We present a new framework for computing resummed and matched distributions in processes with many hard QCD jets. The intricate color structure of soft gluon emission at large angles renders resummed calculations highly non-trivial in this case. We automate all ingredients necessary for the color evolution of the soft function at next-to-leading-logarithmic accuracy, namely the selection of the color bases and the projections of color operators and Born amplitudes onto those bases. Explicit results for all QCD processes with up to $2\to 5$ partons are given. We also devise a new tree-level matching scheme for resummed calculations which exploits a quasi-local subtraction based on the Catani-Seymour dipole formalism. We implement both resummation and matching in the Sherpa event generator. As a proof of concept, we compute the resummed and matched transverse-thrust distribution for hadronic collisions.