Measurements of $ZZ \rightarrow \ell\ellνν$ and $ZZjj \rightarrow \ell\ellννjj$ productions in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This ATLAS study measures $ZZ$ production in $pp$ collisions at $\sqrt{s}=13$ TeV using 140 fb$^{-1}$, focusing on $ZZ\to\ell\ell\nu\nu$ and $ZZjj\to \ell\ell\nu\nu jj$ final states. It reports fiducial cross-sections $\sigma^{\mathrm{fid}}_{ZZ\to \ell\ell\nu\nu}=21.03\pm0.73\mathrm{(stat)}\pm0.57\mathrm{(exp)}\pm0.18\mathrm{(theory)}\pm0.18\mathrm{(lumi)}$ fb and $\sigma^{\mathrm{fid}}_{ZZjj\to \ell\ell\nu\nu jj}=0.96^{+0.15}_{-0.11}\mathrm{(stat)}\pm0.10\mathrm{(exp)}\pm0.04\mathrm{(theory)}\pm0.01\mathrm{(lumi)}$ fb, with a total cross-section $\sigma^{\mathrm{total}}_{ZZ}=15.38\pm0.81$ pb, consistent with SM predictions. Differential cross-sections are unfolded for multiple observables, including a CP-sensitive $\sin(\varphi)\cos(\theta)$ in $ZZ$ and $m_T^{ZZ}$ in $ZZjj$, enabling stringent tests of SM dynamics and parton-shower modeling. The analysis also derives limits on anomalous neutral triple gauge couplings and anomalous quartic gauge couplings using both vertex-function and SMEFT formalisms, achieving improved sensitivity over previous ATLAS results. Overall, the results validate the SM description of diboson processes at high energy and enhance constraints on new electroweak interactions with a large data set and state-of-the-art theory predictions.

Abstract

This article presents measurements of $Z$ boson pair production cross-sections at a center-of-mass energy of $\sqrt{s} = 13$ TeV, using 140 fb$^{-1}$ of proton-proton data collected with the ATLAS detector at the Large Hadron Collider. The analysis includes both inclusive $ZZ$ production and $ZZ$ production in association with two jets ($ZZjj$), where one $Z$ boson decays into a pair of charged leptons $\ell^+\ell^-$ ($\ell = e, μ$), and the other decays into a neutrino pair. The measured fiducial cross-section of the inclusive $ZZ$ production is $21.0\pm1.0$ fb, while for the $ZZjj$ production it is $0.96^{+0.18}_{-0.16}$ fb. Extrapolation of the $ZZ$ cross-section to the full phase space, for $Z$ bosons within the mass range $66-116$~GeV, yields $σ(pp \rightarrow ZZ) = 15.38\pm0.81$ pb. Differential cross-sections are presented for an extended set of kinematic observables. The results are found to be in good agreement with Standard Model predictions. Constraints on anomalous gauge boson self-interactions are derived using both the vertex function formalism and the effective field theory framework.

Figures (12)

• Figure 1: Example of Feynman diagrams for the production of a pair of $Z$ bosons from the (a) $q\bar{q}$ and (b) $gg$ initial states at the LHC. The s-channel diagram (c) is not allowed at LO in the SM; it represents an anomalous triple gauge coupling (aTGC) of a $ZZZ$ or $ZZ\gamma$ vertex.
• Figure 2: Typical diagrams for the production of $ZZjj$ events. The electroweak production, containing triple and quartic interaction vertices, is shown in (a) and (b), while (c) shows the QCD production with gluons in the final state.
• Figure 3: The post-fit distributions of $\Delta\phi(\vec{E}_\text{T}^\text{miss}, Z)$. Panels (a) and (b) show the signal regions for the inclusive $ZZ$ and $ZZjj$ production, respectively. The "Other" category counts events from processes of $ZZ(\rightarrow 4\ell$, $2\ell 2q), VVV (V=W, Z), Wj, Z(\rightarrow \tau\tau), \textrm{and}~ WH$. Panels (c), (d) and (e) illustrate the background CRs for inclusive $ZZ$ production, while panels (f) and (g) display the $ZZjj$ CRs. Panel (h) presents the post-fit event yields for background events in the $Z$+jets CRs for the inclusive $ZZ$ analysis. Data points are shown with statistical error bars, while the shaded band represents the total post-fit uncertainty in the prediction, combining statistical and systematic uncertainties. Open markers indicate data points lying outside the vertical range of the plot.
• Figure 4: Post-fit kinematic distributions for the inclusive $ZZ$ SR are shown in the top row: (a) the transverse momentum of the leading lepton $p_\text{T}^\text{leading lepton}$, (b) $E_\text{T}^\text{miss}$ and (c) the azimuthal angle separation between two charged leptons $\Delta\phi(\ell, \ell)$. For the $ZZjj$ SR, the bottom row shows: (d) the leading jet $p_\text{T}^\text{leading jet}$, (e) the invariant mass of the dijet system $m_\text{jj}$, and (f) the transverse mass of the $ZZ$ system $m_\text{T}^\text{ZZ}$. The data points are shown with statistical error bars, while the shaded band represents the total post-fit uncertainty in the prediction, combining statistical and systematic uncertainties. Open markers indicate data points lying outside the vertical range of the plot.
• Figure 5: Differential cross-section measurements in the inclusive $ZZ\rightarrow \ell\ell\nu\nu$ fiducial phase space, compared with MC predictions calculated with the nominal Sherpa simulation and with Matrix for a set of kinematic variables: (a) $p_\text{T}^\text{leading lepton}~, \text{(b)}~ p_\text{T}^\text{Z}~, \text{(c)}~\Delta\phi(\ell, \ell),~ \text{(d)}~|y^Z|,~ \text{(e)}~ p_\text{T}^\text{ZZ},~ \text{(f)}~ m_\text{T}^\text{ZZ},~ \text{(g)}~ N_{\text{jets}}$, and (h) a CP-sensitive angular variable, $\sin(\varphi)\cos(\theta)$. The statistical and total uncertainties in the data points are displayed in both the differential cross-sections and the corresponding ratios. The total theory uncertainties in the Sherpa and Matrix predictions are represented as shaded bands in the cross-section panels and as error bars in the ratio panels.