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Browsing OU - Dissertations by Author "Abbott, Brad"
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Item Open Access The dark universe: the interplay of cosmological moduli, axions, and the MSSM(2023-05) Wiley Deal, Robert; Baer, Howard; Sinha, Kuver; Abbott, Brad; Mullen, Kieran; Przebinda, TomaszIn this work, we introduce two effective field theories which parameterize a light modulus field interacting both with the MSSM ($\phi$MSSM) and with the MSSM combined with an additional supersymmetric DFSZ axion ($\phi$PQMSSM). All two-body decays of the modulus are cataloged and connected to explicit string scenarios, with all model-independent decay widths calculated incorporating mixing and phase-space effects for the first time. Dark matter and dark radiation production are studied in both models for a subset of string scenarios, with comments provided on expectations for the remaining scenarios. Quite generally, we find that many string scenarios with a modulus-driven early matter dominated period overproduce dark matter and/or dark radiation. The overproduction of dark matter may be remedied with a sufficiently large modulus mass, however various consistency conditions show that most scenarios are incompatible with weak-scale supersymmetry and with a DFSZ-type axion, at least without additional model-building. We also study statistical properties of the Peccei-Quinn scale $f_a$ and the derived value of the SUSY $\mu$-term in the string landscape. Here, we find the predicted value of $f_a$ is in the cosmological sweet-spot for axion dark matter, while the predicted higgsino masses are slightly above current LHC bounds. Additionally, we study the predicted nature of viable dark matter candidates in explicit inflationary scenarios in string theory, finding a WIMP in K\"{a}hler inflation and open string axions in fibre inflation to be natural dark matter candidates.Item Open Access MEASUREMENT OF THE INCLUSIVE ISOLATED PROMPT PHOTON PRODUCTION AT sqrt{s} = 7 TeV WITH THE ATLAS DETECTOR FOR THE 2011 DATASET(2014-12) Norberg, Scarlet; Abbott, Brad; Palmeri, JoAnn; Baer, Howard; Gutierrez, Phillip; Murphy, SheenaA measurement of the cross section for the inclusive production of isolated prompt photons in $pp$ collisions at a center-of-mass energy $\sqrt{s} = 7\TeV$ is presented. The measurement covers the pseudorapidity ranges $|\eta^\gamma|<1.37$ and $1.52\leq|\eta^\gamma|<2.37$, in the transverse energy range $100\leq\ET^{\gamma}<1000 \GeV$. The results are based on an integrated luminosity of 4.6~\ifb\ collected with the ATLAS detector at the LHC. The results are compared with next-to-leading order perturbative QCD calculations with CT10 and MSTW2008NLO PDFs, as well as two leading order Monte Carlo PYTHIA and HERWIG.Item Open Access SEARCH FOR SUPERSYMMETRY IN FINAL STATES WITH TWO SAME SIGN LEPTONS OR THREE LEPTONS AND JETS WITH THE ATLAS DETECTOR AT THE LHC(2017-07-07) Rifki, Othmane; Abbott, Brad; Abraham, Eric; Barker, Peter; Strauss, Michael; Kao, ChungThe Standard Model of particle physics is the culmination of decades of experimental and theoretical advancements to successfully describe the elementary particles and their interactions at low energies, up to 100 GeV. Beyond this scale lies the realm of new physics needed to remedy problems that arise at higher energies, the TeV scale and above. Supersymmetry (SUSY) is the most favored extension of the Standard Model that solves many of its limitations, if predicted SUSY particles exist at the TeV scale. The Large Hadron Collider (LHC) at CERN has opened a new phase of exploration into new physics at the TeV scale after increasing the center-of-mass energy of the proton-proton collisions to 13 TeV. The ATLAS experiment has collected this collision data with over 90% efficiency due to the excellent performance of many of its systems, in particular the data acquisition system. The work realized and described in this dissertation ensures the efficient collection of ATLAS data as well as the analysis of this data to search for SUSY. The first part is devoted to the migration of the functionality of the multi-card custom electronics Region of Interest Builder (RoIB), a central part of the data acquisition system which processes every event recorded by ATLAS, to a single PCI-Express card hosted in a commodity computing node. This evolution was undertaken to increase the system flexibility and reduce the operational overload associated with custom electronics. The second part deals with the search for strongly produced supersymmetric particles decaying into final states with multiple energetic jets and either two leptons (electrons or muons) with the same electric charge or at least three leptons using the whole proton-proton collision dataset of 36 fb-1 at 13 TeV recorded with the ATLAS detector in 2015 and 2016. The analysis pioneers the search for supersymmetry with a novel experimental signature of three leptons of the same electric charge. Due to the low Standard Model background, these final states are particularly adapted to searches for gluinos or third generation squarks in several SUSY production topologies determined from a variety of simplified and phenomenological models. The main aspects of the analysis are described, in particular the methods used to estimate the various backgrounds that come from known Standard Model production processes with a final state similar to the SUSY models being targeted, as well as detector measurement effects. The absence of excess over the Standard Model prediction is interpreted in terms of limits on the masses of superpartners derived at 95% confidence level. In the studied decay modes and depending on the decay topology, the existence of gluinos with masses below 1.9 TeV, sbottoms with masses below 700 GeV, and neutralinos with masses below 1.2 TeV are excluded.