Abstract
We compute next-to-leading order (NLO) QCD corrections to the production of two massive electroweak bosons in gluon fusion. We consider both the prompt production process $gg \to VV$ and the production mediated by an exchange of an s-channel Higgs boson, $gg \to H^* \to V V$. We include final states with both on- and off-shell vector bosons with leptonic decays. The gluonic production of vector bosons is a loop-induced process, including both massless and massive quarks in the loop. For $gg \to ZZ$ production, we obtain the NLO QCD corrections to the massive loops through an expansion around the heavy top limit. This approximation is valid below the top production threshold, giving a broad range of invariant masses between the Higgs production and the top production thresholds in which our results are valid. We explore the NLO QCD effects in $gg \to ZZ$ focusing, in particular, on the interference between prompt and Higgs-mediated processes. We find that the QCD corrections to the interference are large and similar in size to the corrections to both the signal and the background processes. At the same time, we observe that corrections to the interference change rapidly with the four-lepton invariant mass in the region around the ZZ production threshold. We also study the interference effects in $gg \to WW$ production where, due to technical limitations, we only consider contributions of massless loops. We find that the QCD corrections to the interference in this case are somewhat larger than those for either the signal or the background.
Highlights
Of the off-shell to on-shell cross sections pp → H → ZZ can be used to obtain stringent constraints on the Higgs boson width [4,5,6]
A significant amount of recent effort has been focused on QCD corrections to both Higgs and massive V V production, resulting in the former being computed to next-tonext-to-next-to leading order (N3LO) in QCD in the heavy top limit [17, 18] and the latter to next-to-next-to leading order (NNLO) [19,20,21,22,23]
This observation suggests a way of estimating the impact of next-to-leading order (NLO) QCD corrections to the interference including all quark flavors, by adding the NLO results displayed in figure 9 to the LO third generation contribution multiplied by the approximate K-factor KbkgdKsignal = 1.6
Summary
These checks of the implementation still leave as an open question whether the 1/mt expansion of physical cross sections for ZZ production in gluon fusion converges To investigate this issue, we begin at LO, where we can perform a comparison of exact and expanded in 1/mt contributions to prompt production of Z-pairs. We conclude this section by stressing that in this paper we are mostly interested in genuine NLO corrections to the gg → 4l process As a consequence, this relatively hard upper cut on jet emission is not relevant for us, since in the region p⊥j > pm⊥,ajx our computation is only LO and if desired the result in this region can be obtained using automatic one-loop frameworks, see e.g. This relatively hard upper cut on jet emission is not relevant for us, since in the region p⊥j > pm⊥,ajx our computation is only LO and if desired the result in this region can be obtained using automatic one-loop frameworks, see e.g. [46, 52]
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