CPPM, Aix-Marseille Université and CNRS/IN2P3, Marseille, France.
Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma, USA.
Phys Rev Lett. 2014 Jun 13;112(23):231806. doi: 10.1103/PhysRevLett.112.231806.
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.
呈现了在 LHC 上 pp 碰撞中利用 ATLAS 探测器测量 Z 共振处的四轻子（4ℓ，ℓ=e，μ）产生截面。在轻子对和四轻子不变质量区域 m(ℓ+ℓ(-)) > 5 GeV 和 80<m(4ℓ) < 100 GeV 中，测量到的截面分别为在 sqrt[s] = 7 TeV 和 8 TeV 时为 76 ± 18(stat) ± 4(syst) ± 1.4(lumi) fb 和 107 ± 9(stat) ± 4(syst) ± 3.0(lumi) fb。通过减去非共振 4ℓ 产生贡献，并利用 Z → μ(+)μ(-)事件归一化，确定 Z 玻色子衰变为 4ℓ 的分支比为 (3.20 ± 0.25(stat) ± 0.13(syst)) × 10(-6)，与标准模型预测一致。
