W+W-, WZ and ZZ production in the POWHEG BOX V2

TL;DR

The paper presents a new POWHEG BOX V2 implementation for vector boson pair production (ZZ, W+W-, WZ) that supports all decay modes and mixing of decay channels in a single run, with substantial speed and phase-space enhancements and refined interference treatment. It relies on MCFM-based matrix elements extended to hadronic decays, includes CKM handling and hadronic decay corrections, and integrates resonance-aware radiation strategies suitable for shower MCs. Key innovations include reorganized interference calculations, Lorentzian importance sampling for single-resonant regions, and a new upper-bound radiation consolidation across equivalent amplitudes to boost efficiency. The work delivers a flexible, efficient, and accurate tool for NLO-QCD predictions of vector boson pairs at colliders, ready for interfacing with parton showers and experimental analyses.

Abstract

We present an implementation of the vector boson pair production processes ZZ, W+W- and WZ within the POWHEG BOX V2. This implementation, derived from the POWHEG BOX version, has several improvements over the old one, among which the inclusion of all decay modes of the vector bosons, the possibility to generate different decay modes in the same run, speed optimization and phase space improvements in the handling of interference and singly resonant contributions.