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 qq-, 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 qq- 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).
Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Aben, R., Abolins, M., et al. (2016). Measurements of four-lepton production in pp collisions at √s = 8 TeV with the ATLAS detector. PHYSICS LETTERS. SECTION B, 753, 552-572 [10.1016/j.physletb.2015.12.048].