アイテム詳細

要旨

Various theories beyond the Standard Model of particle physics include an extended Higgs sector with at least one pair of charged Higgs bosons. For charged Higgs bosons with a mass m(H±) > m(t) + m(b), the dominant production mode is in association with a top and bottom quark (tbH±). In the alignment limit of the Two Higgs-Doublet Model (2HDM) a significant decay channel is also constituted by H± → W ±H, the decay into a non-SM heavy neutral Higgs boson and a W boson. However, this decay is so far only minimally covered by previous searches at the Large Hadron Collider. In this thesis, different Monte Carlo generator setups for the H± signal generation are tested and the setup considering the W boson polarization is used to generate the charged Higgs boson signal in H± → W ±H → l±νbb decays. These samples are then utilised to optimise the search strategy for this decay channel. A search strategy based on Boosted Decision Trees (BDTs) is outlined and tested. BDTs are applied to reconstruct the charged Higgs boson candidates by selecting the right jet combinations from a final state containing one charged lepton, multiple jets, and missing transverse momentum. The challenge of this method is to identify the two jets originating from the neutral Higgs boson decay (H → b¯b) among the other jets stemming from the tbH± production or an hadronic W boson decay. The BDT performance is evaluated in terms of fractions of correctly reconstructed candidates and the resolution of the reconstructed charged Higgs boson mass. The dominating t¯t-background is simulated at ATLAS Run 2 conditions with an integrated luminosity of 140 fb−1 at a proton-proton centre of mass energy of √s = 13 TeV. The search sensitivity for the signal against this background is estimated by determining upper limits on the cross section times branching ratio of the pp → tbH± → tb W ±H → tb l±νbb process. The expected upper limits at a 95% confidence level range from (85.3 ± 1.5) fb at m(H±) = 300 GeV to (14.8 ± 0.3) fb at m(H±) = 700 GeV.