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

Abstract

We implement the recently-calculated analytic expressions for the next-to-leading order QCD corrections to $gg\to ZH$ 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.

Figures (11)

• Figure 1: Sample Feynman diagrams with quarks or anti-quarks in the initial state. The Drell Yan-type contributions (a) are not included in ggxy. Using the switch iopt_ext_Z it is possible to include either all contributions from (b)-(e) or only those where both bosons couple to the fermion loop, see (b) and (c).
• Figure 2: Ratio of the finite virtual corrections ${\cal V}_{\rm fin}$ obtained from ggxy and Ref. Chen:2020gae ("PSD") as a function of $p_T$. The statistical uncertainties of the reference results are shown as well.
• Figure 3: $M_{ZH}$ invariant mass and $Z$ boson transverse momentum distribution for stable $Z$ bosons. The input parameters from Ref. CampilloAveleira:2025rbh have been adapted.
• Figure 4: Comparison with Ref. CampilloAveleira:2025rbh for the distributions in $M_{ZH}$ and $p_{T,Z}$. In the lower panels we show the difference of the results normalized to the combined statistical uncertainties.
• Figure 5: Dependence on the top quark mass renormalization scale for the distributions in $M_{ZH}$ and $p_{T,H}$. In the lower panels we show the ratios between the different choices of $\overline{\text{MS}}$ scales to the on-shell scheme for fixed $\mu_f=\mu_r=M_{ZH}/2$.