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A Search for Evidence of New Particle Production in Pp Collisions at Sqrt(s) = 8 TeV in the Lepton, Jets, and Photons Final State

Francis, Brian
Thesis/Dissertation; Online
Francis, Brian
Cox, Bradley
This dissertation presents a search for evidence of new particle production in the one- and two-photon, lepton, and b-jet final state in proton-proton collisions at center-of-mass energy 8 TeV. The search is performed in the full 2012 dataset, a total integrated luminosity of 19.7/fb, collected by the Compact Muon Solenoid experiment at the Large Hadron Collider. A substantial imbalance in the transverse momentum of observed particles (missing transverse energy) in this final state would result from the theory of Supersymmetry, the fundamental symmetry of spin which may provide a solution to the hierarchy problem of particle physics. The presence of third-generation quark decays and photons in the final state are motivated by gauge-mediated models of Supersymmetry, and in particular by models which solve the hierarchy problem most naturally. The expected background distribution of missing transverse energy in these events, dominated by ttbar + photon and ttbar + di-photon production, is simulated in Monte Carlo and compared to the observed distribution in data. No significant excess of large missing transverse energy is observed. Upper limits on the cross sections of scalar top pair production are set at the 95% confidence level between 5 and 15 fb. The results of this search are among the first within gauge-mediated models of Supersymmetry with a light scalar top and places extraordinarily tight constraints on such models by excluding scalar top masses below 650-750 GeV/c^2.
University of Virginia, Department of Physics, PHD (Doctor of Philosophy), 2015
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PHD (Doctor of Philosophy)
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