<p> This dissertation describes a search for charged Higgs bosons decaying to a tau and a neutrino (<i>H</i><sup>+</sup> → τ<sup> +</sup> ν<sub>τ</sub>) or the charge-conjugate process) in association with a leptonically decaying top quark, using 36.1 fb<sup>–1</sup> of <i>pp</i> collision data collected with √s = 13 TeV by the ATLAS detector. The theoretical motivation, including a review of the Standard Model, is given, along with a description of the ATLAS detector and particle reconstruction. A multi-variate analysis approach uses stochastic gradient boosted decision trees to improve the separation between <i> H</i><sup>±</sup> signal and background. The semi-leptonic channel described in this thesis is used in combination with a fully hadronic channel to search for charged Higgs bosons in a mass range of 90 GeV ≤ <i> m<sub>H</sub></i>± 2000 GeV. Finding no significant excess, limits are set at the 95% confidence level on the charged Higgs production cross section times the branching fraction into τν ranging from 4.2 pb to 2.5 fb. These limits are interpreted in the hMSSM benchmark scenario as an exclusion at 95% confidence on tan β as a function of <i> m<sub>H</sub></i>±. In this scenario, for tan β = 60, the <i> H</i><sup>±</sup> mass range up to 1100 GeV is excluded, with all values of tan β exclude for <i>m<sub>H</sub></i>± ≤160 GeV</p><p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:10839888 |
| Date | 05 January 2019 |
| Creators | Burghgrave, Blake |
| Publisher | Northern Illinois University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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