Search for heavy Higgs bosons in lepton + jets final states with the ATLAS detector at the Large Hadron Collider

Abstract

This thesis presents a search for heavy Higgs bosons in the context of new physics, e.g. the Two-Higgs Doublet Model (2HDM). The considered signal scenarios of , , and were searched in the “lepton + jets” final states. The analysis uses Monte Carlo generated samples that corresponds to 36.5/fb of data at a center-of-mass energy of 13 TeV. The discrimination between signal and background events was done by a multivariate classifier acquired by training a Boosted Decision Tree (BDT). A profile likelihood ratio, constructed from Poisson probability terms, was used in the modified frequentist CLs technique in order to calculate the exclusion limits at a 95% confidence level on the product of the production cross-section and the branching ratio for each signal scenario at the mass points of 400, 600, 800, and 1000 GeV. The experimental results show that the BDT output has good separation power between the signal and the background events. The expected limits exclude the mass range of less than 700 GeV and 900 GeV in the low region ( for the neutral Higgs and the charged Higgs bosons respectively. While in the mass range of 400 to 1000 GeV in the moderate = 3 - 10) and high () regions are still open for further research.