Helicity Antenna Showers for Hadron Colliders

TL;DR

This paper introduces helicity-dependent antenna functions for QCD radiation in hadron colliders, implemented in the Vincia Monte Carlo, enabling faster simulations with explicit helicity sampling and improved efficiency in matrix-element corrections.

Contribution

The paper develops and implements a complete set of helicity-dependent antenna functions in Vincia, enhancing simulation speed and accuracy for hadron collider processes.

Findings

Faster evaluation of fixed-order matrix-element corrections.

Implementation of helicity sampling in parton showers.

Comparison shows Vincia 2.200 performs well against Pythia 8.226.

Abstract

We present a complete set of helicity-dependent 2->3 antenna functions for QCD initial- and final- state radiation. The functions are implemented in the Vincia shower Monte Carlo framework and are used to generate showers for hadron-collider processes in which helicities are explicitly sampled (and conserved) at each step of the evolution. Although not capturing the full effects of spin correlations, the explicit helicity sampling does permit a significantly faster evaluation of fixed-order matrix-element corrections. A further speed increase is achieved via the implementation of a new fast library of analytical MHV amplitudes, while matrix elements from Madgraph are used for non-MHV configurations. A few examples of applications to QCD 2->2 processes are given, comparing the newly released Vincia 2.200 to Pythia 8.226.