Search for the Standard Model Higgs boson in $H o ZZ$ decay channels with the ATLAS detector

The Standard Model Higgs boson in the medium and high mass ranges has a large branching ratio for decays to a pair of neutral weak bosons. Three decay modes of the $Z$ boson pair have been explored by ATLAS. One $Z$ is typically produced on-shell, which can be tagged using leptonic decay products. The decay of the second $Z^{(*)}$ boson leads to three independent search channels: $ellell qq$, $ellell u u$ and $ellellellell$. Background compositions and topologies differ among these channels. The $ellell qq$ search can use jet information to reduce top and $Z$+jets backgrounds; the $ellell u u$ search requires a good understanding of missing transverse energy, while the 4 lepton ('golden') channel is almost background-free and, owing to its low production rate, needs excellent lepton efficiencies in order to be sensitive.