Measurements of four-lepton production in pp collisions at √s= 8 TeV with the ATLAS detector

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The four-lepton (4ℓ, ℓ = e, μ) production cross section is measured in the mass range from 80 to 1000 GeV using 20.3 fb⁻¹ of data in pp collisions at √s=8 TeV collected with the ATLAS detector at the LHC. The 4ℓ events are produced in the decays of resonant Z and Higgs bosons and the non-resonant ZZ continuum originating from q q, gg, and qg initial states. A total of 476 signal candidate events are observed with a background expectation of 26.2 ± 3.6 events, enabling the measurement of the integrated cross section and the differential cross section as a function of the invariant mass and transverse momentum of the four-lepton system. In the mass range above 180 GeV, assuming the theoretical constraint on the q q production cross section calculated with perturbative NNLO QCD and NLO electroweak corrections, the signal strength of the gluon-fusion component relative to its leading-order prediction is determined to be μgg=2.4 ± 1.0 (stat.) ± 0.5 (syst.)± 0.8 (theory).