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Measurements of Four-Lepton Production at the Z Resonance in pp Collisions at sqrt[s]=7 and 8 TeV with ATLAS.

Aad, G; Abbott, B; Abdallah, J; Abdel Khalek, S; Abdinov, O; Aben, R; Abi, B; Abolins, M; AbouZeid, O S and Abramowicz, H, et al. (2014) In Physical Review Letters 112(23).
Abstract
Measurements of four-lepton (4ℓ, ℓ=e,μ) production cross sections at the Z resonance in pp collisions at the LHC with the ATLAS detector are presented. For dilepton and four-lepton invariant mass regions m_{ℓ^{+}ℓ^{-}}>5 GeV and 80<m_{4ℓ}<100 GeV, the measured cross sections are 76±18(stat)±4(syst)±1.4(lumi) fb and 107±9(stat)±4(syst)±3.0(lumi) fb at sqrt[s]=7 and 8 TeV, respectively. By subtracting the nonresonant 4ℓ production contributions and normalizing with Z→μ^{+}μ^{-} events, the branching fraction for the Z boson decay to 4ℓ is determined to be (3.20±0.25(stat)±0.13(syst))×10^{-6}, consistent with the standard model prediction.
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