Next-to-leading order QCD corrections to Z boson pair production via vector-boson fusion

TL;DR

This paper delivers the first NLO QCD calculations for electroweak ZZ production in vector-boson fusion with two tagging jets and leptonic Z decays, implemented in a flexible parton-level Monte Carlo for pp -> e+ e- mu+ mu- jj and pp -> e+ e- nu_mu nubar_mu jj at order $\alpha_s\alpha^6$. The authors employ a comprehensive treatment of t-channel weak-boson exchange, finite-width effects via a complex-mass scheme, and advanced techniques for real and virtual corrections, including dipole subtraction and pentagon-tensor reductions, with extensive validation. They find integrated cross sections largely unchanged by NLO corrections (K ~ 0.99) and small scale uncertainties, while certain differential distributions exhibit notable shape changes and dynamical K-factors (0.8–1.4), underscoring the importance of NLO accuracy for precision studies of electroweak symmetry breaking at the LHC.

Abstract

Vector-boson fusion processes are an important tool for the study of electroweak symmetry breaking at hadron colliders, since they allow to distinguish a light Higgs boson scenario from strong weak boson scattering. We here consider the channels WW->ZZ and ZZ->ZZ as part of electroweak Z boson pair production in association with two tagging jets. We present the calculation of the NLO QCD corrections to the cross sections for p p -> e+ e- mu+ mu- + 2 jets and p p -> e+ e- nu_mu nubar_mu + 2 jets via vector-boson fusion at order alpha_s alpha^6, which is performed in the form a NLO parton-level Monte Carlo program. The corrections to the integrated cross sections are found to be modest, while the shapes of some kinematical distributions change appreciably at NLO. Residual scale uncertainties typically are at the few percent level.

Figures (4)

• Figure 1: The six Feynman-graph topologies contributing to the Born process $uc\,\hbox{$\rightarrow$}\, uc\,e^+e^- \,\mu^+\mu^-$. Diagrams analogous to (a), (d), (e) and (f), with vector-boson emission off the lower quark line, are not shown.
• Figure 2: Scale dependence of the total EW $e^+e^- \,\nu_\mu \bar{\nu}_\mu\,jj$ cross section at LO and NLO within the cuts of Eqs. (\ref{['eq:cutspj']})--(\ref{['eq:offres']}) for $pp$ collisions at the LHC. The NLO curves show $\sigma_{\rm cuts}^{\rm NLO}$ as functions of the scale parameter $\xi$ for three different cases: $\mu_F=\mu_R=\xi m_Z$ (solid red), $\mu_F=\xi m_Z$ and $\mu_R=m_Z$ (dot-dashed blue), $\mu_F=m_Z$ and $\mu_R=\xi m_Z$ (dashed green). The LO cross section depends only on $\mu_F$ (dotted black line).
• Figure 3: Invariant-mass distribution of the tagging jets in EW $e^+e^- \,\mu^+\mu^-\,jj$ production at the LHC. Panel (a) shows the NLO (solid red) and the LO results (dashed black). Panel (b) displays the K factor as defined in Eq. (\ref{['eq:kfac']}).
• Figure 4: Panel (a): distribution of the four lepton invariant mass in EW $e^+e^- \,\mu^+\mu^-\,jj$ continuum production at the LHC, within the cuts of Eqs. (\ref{['eq:cutspj']})--(\ref{['eq:offres']}) with $m_H=120$ GeV. Panel (b) shows the same observable when the contribution from a Higgs boson of mass $m_H=500$ GeV is included. In each case, NLO (red solid) and LO (black dashed) results are shown.