UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
4 results
Search Results
Item Search for emerging-jet signatures in pp collisions at 13 TeV with CMS using a fully data-based method for background extraction(2023) Chen, Yi-Mu; Belloni, Alberto; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)For this thesis, I present a search for emerging jets produced in proton-proton collisions at a center-of-mass energy of 13 TeV. This search examines a hypothetical dark QCD sector that couples to the standard model through a scalar mediator. The scalar mediator decays into a standard model quark and a dark sector quark. As the dark sector quark showers and hadronizes, it produces long-lived dark mesons that subsequently decay into SM particles, resulting in a jet with multiple displaced vertices, known as an emerging jet. This search extends the existing efforts of CMS by including the possibility of a flavored coupling between the standard model sector and dark sector, which results in emerging jets containing both long-lived and prompt decays. This search looks for pair production of the scalar mediators at the LHC, yielding events with two SM jets and two emerging jets. As the detector signature left by such dark sector showers significantly deviates from the assumptions made when designing the detector, a fully data-based method is used for evaluating the number of standard model events that can be mistaken as signal events. The search is carried out on data collected by the CMS experiment corresponding to an integrated luminosity of 138 /fb , and we observe no significant excess. The results are interpreted using two dark sector models and exclude mediator masses up to 1750 GeV for an unflavored dark QCD model and up to 2000 GeV for a flavored-aligned dark QCD model.Item Search for Pair Production of Third-Generation Scalar Leptoquarks and R-Parity Violating Top Squarks in Proton-Proton Collisions at sqrt(s) = 8 TeV(2014) Pedro, Kevin; Eno, Sarah; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents a search for pair production of third-generation scalar leptoquarks or top squarks in R-parity violating supersymmetry decaying through the coupling λ′333, with the new scalar particle decaying to a tau lepton and a bottom quark. The data used in this search were collected by the Compact Muon Solenoid experiment and comprise 19.7 fb-1 of proton-proton collision data from the Large Hadron Collider at a center-of-mass energy of √(s) = 8 TeV. No excess of events above the standard model background prediction is observed. The existence of third-generation scalar leptoquarks or top squarks with masses below 740 GeV is excluded at the 95% confidence level, assuming the branching fraction for the decay to a tau lepton and a bottom quark is 100%. This is currently the strongest limit on this kind of leptoquark or top squark. The search is extended to address a chargino-mediated decay of the top squark involving the R-parity violating coupling λ′3jk, producing a tau lepton, a bottom quark, and two light quarks. The existence of top squarks in this model with masses below 580 GeV is excluded at the 95% confidence level. This is the first search for the pair production of top squarks with the decay involving the R-parity violating coupling λ′3jk.Item Search for Pair Production of First-Generation Scalar Leptoquarks in Proton-Proton Collisions at √s=7 TeV(2011) Ferencek, Dinko; Eno, Sarah C; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A search for pair production of first-generation scalar leptoquarks in a final state containing an electron, a neutrino, and at least two jets is performed using proton-proton collision data at √s=7 TeV. The data corresponding to an integrated luminosity of 36 pb-1 were collected by the CMS detector at the CERN LHC. The number of observed events is in good agreement with the predicted yield for Standard Model processes. Prior results from CMS in the dielectron channel are combined with this electron+neutrino search. A combined 95%-confidence-level lower limit of 339 GeV is set on the mass of a first-generation scalar leptoquark for β of 0.5, where β is the branching ratio for the leptoquark to decay to an electron and a quark. These results represent the most stringent direct limits to date for values of β greater than 0.35.Item SEARCH FOR FIRST GENERATION SCALAR LEPTOQUARKS WITH THE CMS DETECTOR AT THE LARGE HADRON COLLIDER(2011) Twedt, Elizabeth Walsh; Baden, Andrew; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Leptoquarks are particles predicated to exist by many models beyond the standard model. A search is presented for the production of first generation scalar leptoquarks with a branching ratio into charged leptons of β = 1 with the Compact Muon Solenoid detector at the Large Hadron Collider at CERN, at a center of mass energy of 7 TeV.