Heavy Higgs Boson Search Via H Za Zzh

The discovery of a 125GeV Higgs boson at the Large Hadron Collider strongly motivates direct searches for additional Higgs bosons. This thesis describes a search for additional Higgs bosons via Higgs cascade production gg -> H-> ZA ->ZZh, including my phenomenology work as well as the experimental result using proton-protoncollision data collected at [square root s] = 13 TeV with the CMS experiment at the CERN LHC. In type I two Higgs doublet models there is a large region of parameter space at tan [beta] [greater than or similar to] 5 that is currently unconstrained experimentally. The phenomenology shows that the process gg -> H-> ZA ->ZZh can be sensitive in this region,and can be the discovery mode for an extended Higgs sector at the LHC. There are totally 9 promising decay modes for the ZZh state, and the most sensitive final states are [ell][ell][ell][ell]bb, [ell][ell]jjbb, [ell][ell][nu][nu][gamma][gamma] and [ell][ell][ell][ell] + missing energy. The result is presented in terms of 14 TeV projection with integrated luminosity of 300 fb−1 and 3000 fb−1 . The experimental analysis considers the four-lepton and two b-tagged jets final state, resulting from leptonic decays of the two Z bosons and decay of the Higgs bosons to b-quarks, which was found to be the mostsensitive channel in the phenomenological study. The data used in the analysis was collected by the CMS experiment from 35.9 fb−1 of proton-proton collisions at [squareroot s] =13 TeV produced at the Large Hadron Collider in 2016. Upper limits at 95% confidence level are obtained on the cross section of ZZh production in Type I 2HDM scenarios. The cascade decay channel considered in this analysis adds unique sensitivity to some regions of the parameter space within the two-Higgs-doublet-model.