Study of the inclusive four-lepton lineshape in proton-proton collisions at $\sqrt{s}=8$ TeV with the ATLAS detector at the LHC

The inclusive four-lepton lineshape is studied using data corresponding to $20.3$ fb$^{-1}$ of integrated luminosity from proton-proton collisions at $\sqrt{s}=8$ TeV at the LHC collected with the ATLAS detector. The mass spectrum is analyzed in the range $80$--$1000$ GeV, where several distinct physics processes contribute. These include the single resonant processes $qq\rightarrow Z\rightarrow 4\ell$, Higgs production $gg\rightarrow H\rightarrow ZZ^*\rightarrow 4\ell$, as well as continuum $ZZ$ production processes $qq\rightarrow ZZ^* 4\ell$ and $gg\rightarrow ZZ^* \rightarrow 4 \ell$. A total of $476$ four-lepton events are found in the signal region, allowing for a measurement of the total cross section, as well as the differential cross section versus the four-lepton invariant mass. In addition, the first measurement is made of the non-resonant gluon-gluon fusion component in the four-lepton mass region where both $Z$ bosons are produced on shell.