| As described in the “Brief introduction to the Higgs Boson”, the H → WW decay branching ratio for the Higgs boson with a mass of 125 GeV is predicted to be 0.214 in the SM, and corresponds to the second-largest branching fraction after the dominant H → bb decay mode. The predicted Higgs-boson production cross sections via the dominant gluon–gluon fusion (ggF) and vector-boson fusion (VBF) times H → WW branching fraction are 10.4 pb and 0.81 pb for ggF and VBF, respectively. Reducing the numerous backgrounds contributing to this channel and accurately estimating the remainder is a major challenge in this analysis. |
The search for the Higgs through the decay H → ZZ → 4l, where l = e or μ, represents the so called “golden channel” and leads to a narrow four-lepton invariant-mass peak on top a relatively smooth and small background, largely due to the excellent momentum resolution of the ATLAS detector. The Higgs-boson decay branching ratio to the four-lepton final state for the Higgs boson mass of 125 GeV is predicted to be 0.0124% in the SM, and the expected cross section times branching ratio for the process H → ZZ → 4l is 2.9 fb at 13 TeV. Hence, based on an integrated luminosity of the current ATLAS Open Data set of 10/fb, one expects 29 events to have been produced in the final state. |
The H → yy decay mode provides a very clear and distinctive signature of two isolated and highly energetic photons, and is one of the main channels studied at the LHC. Despite the small branching ratio, a reasonably large signal yield can be obtained thanks to the high photon reconstruction and identification efficiency at the ATLAS experiment. Furthermore, due to the excellent photon energy resolution of the ATLAS calorimeter, the signal manifests itself as a narrow peak in the diphoton invariant mass spectrum on top of a smoothly falling irreducible background from QCD production of two photons. |
