Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Experimental study of semitauonic B_c decays and development of the Upstream Tracker electronics for the LHCb upgrade(2023) Yang, Zishuo; Jawahery, Abolhassan; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The LHCb experiment at the Large Hadron Collider is designed for studying the properties of heavy quarks and CP violation to indirectly search for new physics beyond the Standard Model. The first topic of this dissertation is a study of semitauonic B_c meson decays at LHCb to test the universality of the couplings of charged leptons in electroweak interactions, which is known as lepton flavor universality in the Standard Model. The second topic of this dissertation is the development of readout electronics for a new silicon-strip tracking detector, the Upstream Tracker, to upgrade the LHCb detector. The upgraded LHCb detector will collect much more data in the upcoming runs of the Large Hadron Collider.Item Study of the decay B+ → K+ π0 at LHCb and mechanical development for the design of the Upstream Tracker(2018) Andrews, Jason Emory; Jawahery, Abolhassan; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The LHCb experiment at the Large Hadron Collider (LHC) is designed to measure the properties of particles containing charm (c) and bottom (b) quarks. This dissertation documents two major studies I have completed, one analyzing data collected by the LHCb detector, and another contributing to the design and development of an extensive upgrade to the detector. The pattern of CP asymmetry measurements of the B → K π family of decays deviates from expectations derived from the SM, a contradiction known as the “K π puzzle.” The present size of the experimental errors are such that more precise measurements in the B+ → K+ π0 decay channel are especially important. An analysis of the B+ → K+ π0 decay using data collected during Run 1 is performed. Despite low reconstruction and trigger efficiencies and enormous combinatorial backgrounds, a signal is found with a statistical significance of 3.7σ. This achievement has led to the creation of a dedicated B+ → K+ π0 trigger, and has inspired the creation of a number of dedicated triggers for decay modes with similar topologies. A preliminary analysis of data collected during Run 2 demonstrates that the new trigger is a major success, with excellent prospects for making the world’s best measurements in the B+ → K+ π0 decay channel using the entire Run 2 data set. Run 2 of the LHC will conclude at the end of 2018, and will be followed by Run 3, scheduled to begin in early 2021. In the interim, the LHCb detector will be upgraded to be read-out in real-time at 40 MHz, and to withstand the radiation damage associated with collecting 50 fb^(−1) of integrated luminosity by the conclusion of Run 4. A key part of this upgrade is the design and construction of a new silicon-strip tracking detector—the upstream tracker (UT). Regions at the periphery of the UT suffer from severe electrical and mechanical constraints, making a high-fidelity CAD model a critical element of the design process. The result is a mechanical integration solution that is entirely non-trivial, and which has had significant influences on the UT design. This solution and the constraints that influence it are shown in detail.Item SEMITAUONIC B_c^+ DECAYS AND QUARK FLAVOR IDENTIFICATION METHODS(2017) Wimberley, Jack; Jawahery, Abolhassan; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The LHCb experiment at the Large Hadron collider is a unique laboratory for studying the properties of heavy quarks. The physics program of the experiment includes studies of CP violation, measurements of CKM matrix parameters, searches for rare decays, quarkonia studies, and other flavor physics, forward physics, and new physics topics. This thesis presents an analysis of the semitauonic branching fraction $\mathcal{B}(B_c^+ \to J/\psi \tau^+ \nu_\tau)$ of the doubly-heavy $B_c^+$ meson, which serves as a powerful probe of the universality of the couplings of leptons ($e$, $\mu$ and $\tau$) in electroweak interactions. The ratio of this branching fraction to the semimuonic branching fraction $\mathcal{B}(B_c^+ \to J/\psi \mu^+ \nu_\mu)$ is measured to be $\mathcal{R}(J/\psi) = 0.71 \pm 0.17 \mathrm{\,(stat)} \pm 0.18\mathrm{\,(syst)}$. A second topic of the thesis is the creation of a new algorithm for tagging the flavor of neutral mesons in CP violation studies, and a powerful method for calibrating these flavor tagging algorithms via binomial regression.