Next-to-next-to-leading order event generation for $Z$ boson pair production matched to parton shower

TL;DR

This paper introduces a state-of-the-art NNLO QCD calculation for Z boson pair production at the LHC, incorporating detailed effects and matched with parton shower simulations, validated against experimental data.

Contribution

It presents the first NNLL' resummation for this process combined with NNLO accuracy and integrates it into the GENEVA framework for realistic event simulation.

Findings

Good agreement with ATLAS and CMS data at 13 TeV.

First NNLL' resummation for Z pair production.

Accurate modeling of spin, interference, and off-shell effects.

Abstract

We present a novel next-to-next-to-leading order (NNLO) QCD calculation matched to parton shower for the production of a pair of $Z$ bosons decaying to four massless leptons, $p p \to \ell^+ \ell^- \ell'^+ \ell'^- + X$, at the LHC. Spin correlations, interferences and off-shell effects are included throughout. Our result is based on the resummed beam-thrust spectrum, which we evaluate at next-to-next-to-leading-logarithmic (NNLL$'_{\mathcal{T}_0}$) accuracy for the first time for this process, and makes use of the GENEVA Monte Carlo framework for the matching to PYTHIA8 shower and hadronisation models. We compare our predictions with data from the ATLAS and CMS experiments at 13 TeV, finding a good agreement.