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, pp→ℓ+ℓ−ℓ′+ℓ′−+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 (NNLLT0′) 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 13TeV, finding a good agreement.
Highlights
Diboson production at the LHC is of paramount importance to the precision study of electroweak (EW) physics in the Standard Model (SM) and beyond, as it directly probes the non-Abelian EW couplings
We focus only on the quark–antiquark channels and neglect the loop-induced gluon fusion channel, which only starts appearing in the calculation at next-to-next-to-leading order (NNLO) and can be added as a nonsingular fixed-order contribution
The latter contribution amounts to ∼ 6% of the total cross section and, as such, its inclusion will be important when comparing to data
Summary
Diboson production at the LHC is of paramount importance to the precision study of electroweak (EW) physics in the Standard Model (SM) and beyond, as it directly probes the non-Abelian EW couplings. Theoretical predictions to Z Z production have been known at NLO in QCD for some time [29,30,31,32,33,34] These were followed by calculations of NLO EW corrections, both for on-shell bosons [35,36,37] and for fully leptonic final states [38,39], and more recently combinations of NLO QCD and EW contributions have appeared [40,41]. Since the Geneva method does not need a multi-differential reweighting to reach NNLO accuracy, we are able to include the full off-shell effects and deliver the first NNLOPS calculation for Z Z production.. Additional details concerning the calculation are provided in Appendix A and Appendix B
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