NLO QCD+EW predictions for $2\ell2ν$ diboson signatures at the LHC

TL;DR

The paper delivers fully automated NLO QCD+EW predictions for $2\ell2\nu$ diboson signatures at the LHC, including all off-shell and photon-induced contributions, across both different-flavour and same-flavour lepton final states.Using the Munich/Sherpa+OpenLoops framework, it provides detailed differential results at 13 TeV and investigates the interplay of QCD and EW corrections, highlighting large EW Sudakov effects in high-energy tails and notable photon-induced contributions dependent on the chosen photon PDFs.It discusses the relative merits of additive versus multiplicative combinations of QCD and EW corrections and tests practical approximations such as EW_VI with YFS soft-photon resummation or a QED parton shower, while addressing the subtle renormalization of the electromagnetic coupling in processes with external photons.Overall, the work advances precision diboson predictions as backgrounds for Higgs/BSM analyses and informs the treatment of photon-induced channels and high-energy EW effects in LHC phenomenology.

Abstract

We present next-to-leading order (NLO) calculations including QCD and electroweak (EW) corrections for $2\ell2ν$ diboson signatures with two opposite-charge leptons and two neutrinos. Specifically, we study the processes $pp\to e^+ μ^- ν_{e}\barν_μ$ and $pp\to e^+ e^-ν\barν$, including all relevant off-shell diboson channels, $W^+W^-$, $ZZ$, $γZ$, as well as non-resonant contributions. Photon-induced processes are computed at NLO EW, and we discuss subtle differences related to the definition and the renormalisation of the coupling $α$ for processes with initial- and final-state photons. All calculations are performed within the automated Munich/Sherpa+OpenLoops frameworks, and we provide numerical predictions for the LHC at 13 TeV. The behaviour of the corrections is investigated with emphasis on the high-energy regime, where NLO EW effects can amount to tens of percent due to large Sudakov logarithms. The interplay between $WW$ and $ZZ$ contributions to the same-flavour channel, $pp\to e^+ e^-ν\barν$, is discussed in detail, and a quantitative analysis of photon-induced contributions is presented. Finally, we consider approximations that account for all sources of large logarithms, at high and low energy, by combining virtual EW corrections with a YFS soft-photon resummation or a QED parton shower.

Figures (20)

• Figure 1: Sample of Born diagrams contributing to $2\ell2\nu$ production in the different-flavour case ($\ell\neq \ell^\prime$) and in the same-flavour case ($\ell=\ell^\prime$). Both double-resonant (a,b) and single-resonant (c) diagrams are shown.
• Figure 3: Sample of photon-induced Born diagrams contributing to $2\ell2\nu$ production in the different-flavour case ($\ell\neq \ell^\prime$) and in the same-flavour case ($\ell=\ell^\prime$). Double-resonant (a,b), single-resonant (c) and non-resonant (d) diagrams are shown.
• Figure 5: Sample of one loop diagrams contributing to $2\ell2\nu$ production in the different-flavour case ($\ell\neq \ell^\prime$) and in the same-flavour case ($\ell=\ell^\prime$) in the quark-induced (a-d) and photon-induced (e-h) channels.
• Figure 7: Sample of real emission diagrams contributing to $2\ell2\nu$ production in the different-flavour case ($\ell\neq \ell^\prime$) and in the same-flavour case ($\ell=\ell^\prime$), in the quark--antiquark channel (a), the (anti-)quark--photon channel (b,c) and the photon--photon channel (d).
• Figure 9: Distribution in the transverse momentum of the leading lepton, $p_{\mathrm{T},\ell_1}$, for $pp\to e\xspace^+\mu\xspace^-\nu_{e\xspace}\bar{\nu}_{\mu\xspace}$ at 13 TeV. The left panel shows the absolute predictions and relative corrections with respect to LO (including $\gamma\xspace\gamma\xspace\xspace\to 2\ell2\nu$) for the nominal CT14qed PDF. The bands correspond to factor-two scale variations. The upper-right panel shows the effect, at NLO $\text{QCD\xspace{}$\times$EW\xspace}$ level, of switching off $\gamma$-induced contributions or applying photon densities from different current PDFs, while using quark and gluon densities from the nominal CT14qed set throughout. The lower-right ratio shows the level of agreement of the NLO $\text{QCD\xspace{}$\times$EW\xspace{}$_\text{VI}$}$, $\text{NLO\xspace $\text{QCD\xspace{}$\times$EW\xspace{}$_\text{VI}$}$\xspace}\otimes\text{YFS\xspace{}}$ and $\text{NLO\xspace $\text{QCD\xspace{}$\times$EW\xspace{}$_\text{VI}$}$\xspace}\otimes\text{CSS\xspace{}}$ approximations with the exact NLO $\text{QCD\xspace{}$\times$EW\xspace}$ calculation.