Measurement of the total ZZ production cross section in proton-proton collisions at √s = 8 TeV in 20 fb−1 with the ATLAS detector

The ZZ production cross section has been measured by the ATLAS experiment using the four-lepton decay channel, where the term lepton implies electrons and muons. A data sample of 20.3±0.6 fb−1 collected in pp collisions at √s = 8 TeV at the LHC in 2012 is used. Events are selected by requiring four leptons, forming two opposite-sign same-flavour lepton pairs each with an invariant mass between 66 GeV and 116 GeV. We observe 305 candidate events with a background expectation of 20.4±2.9(stat)±5.0(syst.). The ZZ → l−l+l′−l′+ production cross section is measured to be 20.7+1.3(stat.) ± 0.8(syst.) ± 0.6(lumi.) fb in a −1.2 fiducial phase-space corresponding closely to the acceptance region. After correcting for the ZZ → l−l+l′−l′+ branching fraction and the fiducial acceptance, the total ZZ production cross section is measured to be 7.1+0.5(stat.)±0.3(syst.)±0.2(lumi.) pb, where the total cross −0.4 section is defined by requiring both Z bosons to have an invariant mass between 66 GeV and 116 GeV. This result is consistent with the Standard Model expectation of 7.2+0.3 pb.