Measurements of the inclusive σ(pp→4l) at Z resonance and the BR(Z→4l) with ATLAS

Measurements of inclusive 4$\ell$ ($\ell=e,\mu$) production cross sections at the $Z$ resonance in $pp$ collisions at the LHC with the ATLAS detector are presented. In a phase-space region $m_{\ell^+\ell^-}>4$ GeV and $76 < m_{4\ell} < 106$ GeV, the measured corss sections are $114 \pm 27 (stat) \pm 7(syst) \pm 2(lumi)$ and $150 \pm 13(stat) \pm 7(syst) \pm 5(lumi)$ at $\sqrt s$ = 7 TeV and 8 TeV, respectively. By subtracting the non-resonant 4$\ell$ production contributions and normalizing with $pp\rightarrow Z$ cross section, the branching fraction for the $Z$ boson decay to $4\ell$ is determined to be $\left( 4.2 \pm 0.4 \right) \times 10^{-6}$.