Measurement of the $ZZ$ Production Cross Section in $pp$ Collisions at $\sqrt{s}$ = 13 TeV with the ATLAS Detector

Abstract

The $ZZ$ production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb$^{-1}$ of data recorded with the ATLAS detector at the Large Hadron Collider. The considered $Z$ boson candidates decay to an electron or muon pair of mass 66-116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for $Z$ bosons in the same mass range and of all decay modes, giving $16.7^{+2.2}_{-2.0}$(stat.)$^{+0.9}_{-0.7}$(syst.)$^{+1.0}_{-0.7}$(lumi.) pb. The results agree with standard model predictions.

Figures (2)

• Figure 1: (a) Invariant mass $m_{\ell\ell}$ of the leading-$p_{\mathrm{T},\ell\ell}$ versus the subleading-$p_{\mathrm{T},\ell\ell}$ lepton pair ($\ell\ell$), before the requirement $66~\text{\GeV{}} < m_{\ell\ell} < 116~\text{\GeV{}}$ is applied. The dashed lines indicate this requirement. (b) Invariant mass, (c) transverse momentum, and (d) rapidity of the four-lepton system in selected events. The points represent experimental data. The filled histograms show the signal prediction from simulation, including the $\Pquark\APquark$ and loop-induced $g\xspace g\xspace$-initiated process. The contributions are stacked. In the simulation, the prediction from Powheg + 8 combined with is scaled to the $\mathcal{O}(\alphas^{2})$ prediction. The uncertainties in the simulation are from the same sources as the $C_{Z\xspace Z\xspace}$ uncertainty. In addition, 6% $Z\xspace Z\xspace$ cross-section uncertainty and 5% integrated-luminosity uncertainty are included. The expected background of $0.62^{+1.08}_{-0.11}$ events is not shown as a histogram due to its small size.
• Figure 2: (a) Comparison between measured fiducial cross sections and $\mathcal{O}(\alphas^{2})$ predictions. (b) Total cross section compared to measurements at lower center-of-mass energies by ATLAS, CMS, CDF, and D0 Aad:2012awaCMS:2014xjaChatrchyan:2012sgaAaltonen:2014yfaAbazov:2012cj, and to a prediction from at $\mathcal{O}(\alphas^{1})$ accuracy for the $\Pquark\APquark$-initiated process and at $\mathcal{O}(\alphas^{2})$ accuracy for the loop-induced $g\xspace g\xspace$-initiated process. A full $\mathcal{O}(\alphas^{2})$ prediction (known to improve agreement at $\sqs = 13$) was not yet available for all the different center-of-mass energies. Some data points are shifted horizontally to improve readability. The $Z\xspace Z\xspace$ cross section as function of $\sqrt{s}$ in the range 130--209 was also measured at the LEP 2 $\Ppositron\Pelectron$ collider Schael:2013ita.