Search for New Physics in tt ̅ Final States with Additional Heavy-Flavor Jets with the ATLAS Detector
This doctoral thesis focuses on the search for new phenomena in top-antitop quark (tt) final states with additional b-quark jets at the LHC. It uses the full Run 1 dataset collected by the ATLAS experiment in proton-proton collisions at √s=8 TeV. The final state of interest consists of an isolated lepton, a neutrino and at least six jets with at least four b-tagged jets, a challenging experimental signature owing to the large background from tt+heavy-flavor production. This final state is characteristic of ttH production, with the Higgs boson decaying into bb, a process that allows direct probing of the top-Higgs Yukawa coupling. This signature is also present in many extensions of the Standard Model that have been proposed as solutions to the hierarchy problem, such as supersymmetry or composite Higgs models, which predict the pair production of bosonic or fermionic top quark partners, or the anomalous production of four-top-quark events. All these physics processes have been searched for using an ambitious search strategy that has been developed on the basis of a combination of state-of-art theoretical predictions and a sophisticated statistical analysis to constrain in-situ the large background uncertainties. As a result, the most restrictive bounds to date on the above physics processes have been obtained.
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2 The ATLAS Experiment at the Large Hadron Collider
3 Event Simulation
4 Reconstruction of Physics Objects
5 Common Aspects in Searches for New Physics in tbart Final States with Additional HeavyFlavor Jets
6 Statistical Analysis
7 Searches for New Physics in tbart Final States with Additional HeavyFlavor Jets
Appendix ATiming Performance of the Tile Calorimeterwith Muons from Collision Data
Appendix Bt t + HF Modeling
Appendix CInput Variables to the Neural Networkin the t tH Analysis
Appendix DPostfit Distributions for Kinematic Variables
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algorithm analysis ATLAS collaboration ATLAS detector ATLAS experiment ATLAS Simulation b-tagged b-tagged jets b+btt Vtt tNon-t background prediction BR(T branching ratio C-tagging c+ctt b+btt Vtt calibration calorimeter cell collisions correction cross section data and prediction Data Htt light decay electron EmissT fermions gluon hadronic hep-ex hep-ph hierarchy problem Higgs boson Ht+X Htt light jets interaction jets tt c+ctt JHEP kinematic variables Leading b-jet leading jet light jets tt luminosity Madgraph Q mass Montejo Multijet muon pair production particle jets particles parton shower PhD Thesis Powheg+Pythia Phys Rev pile-up Post-fit Pre-fit reconstruction region resolution reweighting sample Simulation ATLAS Single lepton supersymmetric systematic uncertainties Thesis 8 TeV Thesis Powheg+Pythia Madgraph+Pythia tNon-t Total Bkg top quark Total background Total Bkg unc Total unc tt c+ctt b+btt ttbar Vtt tNon-t Total W boson