Measurement of the $ZZ$ production cross section in proton-proton collisions at $\sqrt s =$ 8 TeV using the $ZZ\to\ell^{-}\ell^{+}\ell^{\prime -}\ell^{\prime +}$ and $ZZ\to\ell^{-}\ell^{+}\nu\bar{\nu}$ channels with the ATLAS detector
JHEP 1701 (2017) 099, 2017.
The collaboration

Abstract (data abstract)
CERN-LHC. Measurements of the cross section for ZZ production using the 4l and 2l2nu decay channels in proton-proton collisions at a centre-of-mass energy of 8 TeV with 20.3 fb^-1 of data collected in 2012. The final states used are 4 electrons, 4 muons, 2 electrons and 2 muons, 2 electrons and missing transverse momentum, and 2 muons and missing transverse momentum (MET). The uncertainty on the global normalisation ("Lumi") is 1.9%. See JHEP 01 (2017) 099 for more details. The 4l channel fiducial region is defined as: - 4e, 4mu or 2e2mu - Ambiguities in pairing are resolved by choosing the combination that results in the smaller value of the sum |mll - mZ| for the two pairs, where mll is the mass of the dilepton system. - ptLepton > 7 GeV (at least one with ptLepton > 24 GeV) - |etaMuon| <2.7, |etaElectron|<2.5 (for all but one electron), |etaElectron|<4.9 (for at most one electron) - Both lepton pairs are required to have invariant mass between 66 and 116 GeV. - min(DeltaR(l,l)) > 0.2. The 2l2nu channel fiducial region is defined as: - 2e+MET or 2mu+MET - ptLepton > 25 GeV - |etaLepton| < 2.5 - mll must be between 76 and 106 GeV - -MET*cos(phi_METZ)>90 GeV, where phi_METZ is the angle between the Z and the MET - |MET - pTZ| / pTZ < 0.4, where pTZ is the transverse momentum of the dilepton system - No events with a jet for which ptJet > 25 GeV and |etaJet| < 4.5 - No events with a third electron (muon) for which ptLepton > 7 (6) GeV - min(DeltaR(l,l)) > 0.3