A hierarchical phase space generator for QCD antenna structures

TL;DR

The paper tackles the challenge of efficiently sampling QCD antenna structures in multi-jet final states by introducing a hierarchical, antenna-based phase-space generator. It derives a density aligned with the antenna function A_{n+2}, decomposed through sequential two-body decays and augmented with soft factors, and offers open- and closed-antenna variants to optimize variance. Numerical studies show that HAAG, particularly with open antennas and multi-channel optimization, achieves substantially better efficiency than SARGE across multi-parton configurations, with favorable scaling as the final-state multiplicity grows. The approach is mass-agnostic, accommodates permutations, and provides detailed algorithms (including inversions and analytic integrals) to reproduce the full antenna density, making it practical for realistic LHC background simulations.

Abstract

We present a ``hierarchical'' strategy for phase space generation in order to efficiently map the antenna momentum structures, typically occurring in QCD amplitudes.