Measurement of the 4l Cross Section at the Z Resonance and Determination of the Branching Fraction of Z -> 4l in pp Collisions at sqrt(s) = 7 and 8 TeV with ATLAS

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 mℓ+ℓ−>5  GeV and 80<m4ℓ<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 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.