Measurements of four-lepton production in $pp$ collisions at $\sqrt{s}=$ 8 TeV with the ATLAS detector

The four-lepton ($4\ell$, $\ell = e, \mu$) production is measured in a mass range from 80 to 1000 GeV using 20.3 fb$^{-1}$ of data in $pp$ collisions at $\sqrt{s}=8$ TeV at the LHC with the ATLAS detector. The $4\ell$ signal events come from the decays of resonant $Z$ and Higgs bosons and the non-resonant $ZZ$ continuum produced from $q\bar q$, $gg$, and $qg$ initial states. A total of 476 signal candidate events is observed with a background expectation of $26.2 \pm 3.6$ 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 $q\bar q$ production cross section calculated with perturbative next-to-next-to leading order (NNLO) QCD and next-to-leading order (NLO) Electroweak corrections, the signal strength of the gluon-fusion component with respect to the leading order (LO) prediction is determined to be $\mu_{gg}=2.4 \pm 1.0 ({\rm stat.}) \pm 0.5 ({\rm syst.})\pm 0.8 ({\rm theory})$.