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

Understand

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.