Measurement of the total ZZ production cross section in the four-lepton channel with 4.7 fb^-1 of ATLAS data

The ZZ production cross section is measured by the ATLAS experiment using the four-lepton decay channel, where the term lepton is used for electrons and muons. A data sample of 4.7 fb−1 collected in pp collisions at √s = 7 TeV at the LHC is used. Events are selected by requiring four leptons with pT > 7 GeV, forming two opposite-sign same-flavour lepton pairs with 66 < ml+l− < 116 GeV, with the leading lepton required to have pT > 20 (25) GeV if it is a muon (electron). We observe 62 candidate events in the acceptance |η| < 2.7 for muons (|η| < 2.47 for electrons) with a background expectation of 0.7 +1.3 -0.7 (stat) +1.3 -0.7 (syst). The fiducial ZZ → l+l−l+l− production cross section is measured to be 21.2 +3.2 -2.7 (stat) +1.0 -0.9 (syst) ± 0.8 (lumi) fb. The total ZZ production cross section measurement, extrapolated from the total to the fiducial phase space and corrected for the ZZ → l+l−l+l− branching fraction, is 7.2 +1.1 -0.9 (stat) +0.4 -0.3 (syst) ± 0.3 (lumi) pb. This is consistent with the Standard Model expectation of 6.5 +0.3 -0.2 pb and confirms our previous measurement performed with the first 1 fb−1 of the present dataset.