Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Physics & Astronomy

First Advisor

Evelyn . Thomson

Abstract

This dissertation presents several searches for supersymmetric partners (superpartners) to Stan- dard Model particles. These analyses are performed using proton-proton collision data from the Large Hadron Collider (LHC) collected by the ATLAS experiment. The B − L Minimal Supersym- metric Standard Model predicts that these superpartners will have small R-parity violating couplings and the lightest superpartner will therefore decay to Standard Model particles. Two searches are presented for pair production of scalar top quarks (stops) which subsequently decay to a b-quark and a charged lepton. Limits are set as a function of the stop decay rate to each lepton flavor. The first analysis, performed with 20.3 fb−1 of √s = 8 TeV data, sets limits on the stop mass between 500 and 1000 GeV, while the second analysis, which used 36.1 fb−1 of √s = 13 TeV data, sets stop mass limits between 900 and 1500 GeV. In both analyses, the best limits are achieved for the scenario where the stop decays to a b-quark and an electron more than 95% of the time. Addition- ally, a search for charged and neutral winos (superpartners to the Standard Model gauge bosons) is presented. One possible decay of the charged wino is to a charged lepton and a Z boson. If the Z then also decays to two charged leptons, the four-vector of the three leptons reconstructs that of the charged wino. In this way, the wino search is performed via a trilepton mass resonance. This search utilizes several reconstruction techniques to have sensitivity to many different charged and neutral wino decays in addition to the trilepton resonance. Stringent limits are set on the wino mass for many possible lepton and boson branching ratios. This analysis uses 139 fb−1 of √s = 13 TeV data and it represents the first trilepton resonance result in the campaign of analyses performed with 13 TeV LHC data.

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