Search for a heavy resonance decaying into two photons in association with b-jets with the atlas detector and constraints on a 2HDM+S model
Date
2022
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Abstract
This thesis consists of two parts. The rst part, a two-Higgs doublet model extended with an additional singlet scalar (2HDM+S) is motivated and discussed. A brief introduction to the model and its parameters space is provided. Constraints are applied to the parameter space of this model in order to accommodate a number of discrepancies in the data that have been interpreted in [1] as the result of the H → Sh decay produced via gluon-gluon fusion and in association with top quarks. Implications on the phenomenology of the heavy pseudo-scalar (A) and charged scalar (H+) are discussed. In particular, the decays A → ZH and H+ → W+H become prominent. This leads to nal states with multiple leptons and b-quarks. The decay A → ZH → ZSh results in the production of a high transverse momentum Z produced in association with a lepton and two b-quarks with little additional jet activity. These predictions are compared to the data with the model's benchmark points. With the parameters obtained here, the model is able to accommodate the features at the LHC reported in [1]. Without varying these parameters additional excesses in the Zb¯b and tt¯invariant mass spectra, and the production of 3 leptons plus two b-tagged jets can be explained assuming mA ≈ 600 GeV. In the second part of this thesis, a search for a heavy resonance decaying into two photons in association with b-tagged jets is presented. The search uses proton proton collision data taken at centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC during 2015 to 2018. The dataset used corresponds to a total of 139 fb−1 integrated luminosity. Three di erent models are tested in this search. A Higgs boson like heavy scalar X produced with top quarks, b quarks or Z boson decaying into b ¯b are examined. Limits on these models are set at 95% CL on the production cross-section times branching ratio into two photons, for masses ranging from 160 GeV-1.6 TeV.
Description
A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, University of the Witwatersrand, 2022
Keywords
ATLAS Detector, Heavy Resonance Decayin, Constraints on a 2HDM+S model