Search for third generation vector-like leptons with the ATLAS detector

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dc.contributor.advisorGutierrez, Phillip
dc.contributor.authorMuse, Joseph
dc.contributor.committeeMemberAbbott, Braden
dc.contributor.committeeMemberSinha, Kuver
dc.contributor.committeeMemberLeighly, Karen
dc.contributor.committeeMemberKornelson, Keri
dc.date.accessioned2022-03-10T18:21:45Z
dc.date.available2022-03-10T18:21:45Z
dc.date.issued2022-03-09
dc.date.manuscript2022-03-09
dc.description.abstractThe Standard Model of particle physics provides a concise description of the building blocks of our universe in terms of fundamental particles and their interactions. It is an extremely successful theory, providing a plethora of predictions that precisely match experimental observation. In 2012, the Higgs boson was observed at CERN and was the last particle predicted by the Standard Model that had yet-to-be discovered. While this added further credibility to the theory, the Standard Model appears incomplete. Notably, it only accounts for 5% of the energy density of the universe (the rest being ``dark matter'' and ``dark energy''), it cannot resolve the gravitational force with quantum theory, it does not explain the origin of neutrino masses and cannot account for matter/anti-matter asymmetry. The most plausible explanation is that the theory is an approximation and new physics remains. Vector-like leptons are well-motivated by a number of theories that seek to provide closure on the Standard Model. They are a simple addition to the Standard Model and can help to resolve a number of discrepancies without disturbing precisely measured observables. This thesis presents a search for vector-like leptons that preferentially couple to tau leptons. The search was performed using proton-proton collision data from the Large Hadron Collider collected by the ATLAS experiment from 2015 to 2018 at center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 139 inverse femtobarns. Final states of various lepton multiplicities were considered to isolate the vector-like lepton signal against Standard Model and instrumental background. The major backgrounds mimicking the signal are from WZ, ZZ, tt+Z production and from mis-identified leptons. A number of boosted decision trees were used to improve rejection power against background where the signal was measured using a binned-likelihood estimator. No excess relative to the Standard Model was observed. Exclusion limits were placed on vector-like leptons in the mass range of 130 to 898 GeV.en_US
dc.identifier.urihttps://hdl.handle.net/11244/334960
dc.languageen_USen_US
dc.subjectParticle Physicsen_US
dc.subjectATLAS Experimenten_US
dc.subjectVector-like Leptonsen_US
dc.subjectMachine Learningen_US
dc.thesis.degreePh.D.en_US
dc.titleSearch for third generation vector-like leptons with the ATLAS detectoren_US
ou.groupDodge Family College of Arts and Sciences::Homer L. Dodge Department of Physics and Astronomyen_US
shareok.orcid0000-0002-2585-3793en_US

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