gg → ZH at NLO matched to parton showers with ggxy and POWHEG

We implement the recently-calculated analytic expressions for the next-to-leading order QCD corrections to gg → ZH in ggxy. This provides a flexible framework for investigating partonic and hadronic cross sections for various top quark mass renormalization schemes. We augment the Z boson with leptonic decays, including spin correlations and off-shell effects, and furthermore provide an interface to POWHEG. This enables simulations with parton showers, performed using Pythia.