Search for heavy resonances decaying into a Z boson and a Higgs boson with the ATLAS detector

The thesis presents a search for a heavy resonance decaying into a Z boson and a Standard-Model-like Higgs boson, with the Z boson decaying into two leptons and the Higgs boson decaying into two b quarks using the data collected from 2015 to 2018 by the ATLAS detector corresponding to an integrated luminosity of 139 fb-1. The search probes the reconstructed invariant or transverse mass distributions of the Zh candidates in a mass range from 220 GeV to 5 TeV. The result of the search is compatible with the Standard-Model prediction, and upper limits at the 95% CL are set on the gluon-gluon fusion production cross sections of a pseudoscalar Higgs boson in the Two-Higgs-Doublet Models and the Drell-Yan production cross sections of a heavy vector boson in the Heavy-Vector-Triplet models. The limits on cross sections are interpreted as constraints on the parameters of various Two-Higgs-Doublet Models. Furthermore, the thesis presents a study about a new analysis approach which uses neural networks to improve the sensitivity of the search. In addition to the resonance search, the thesis also discusses the offline simulation of the ATLAS Level-1 calorimeter trigger.