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| Home > Publications database > Search for Supersymmetric Top-Quark Partners Using Support Vector Machines and Upgrade of the Hadron Calorimeter Front-End Readout Control System at CMS |
| Book/Dissertation / PhD Thesis | PUBDB-2017-01744 |
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2017
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2017-01744
Report No.: DESY-THESIS-2017-014
Abstract: In this thesis a search for direct pair production of supersymmetric top-quark partners as well as work on the upgrade of the front-end readout controller of the Hadron Calorimeter (HCAL) of the Compact Muon Solenoid (CMS) experiment are presented. The most appealing extension of the Standard Model (SM) is supersymmetry (SUSY), relating the integer spin (bosons) and half-integer spin elementary particles (fermions). Supersymmetric top-quark partners (top squark) around and below the TeV energy scale offer a solution to the hierarchy problem. Furthermore, R-parity conserving SUSY models propose a cold dark matter candidate in the form of stable lightest supersymmetric particles (LSP), eg lightest neutralinos. The analysis performed in this thesis is a search for top-squark pair production in a final state consisting of a single isolated lepton, jets, among which at least one is tagged as bottom-quark jet, and large missing transverse energy at the CMS experiment at the CERN Large Hadron Collider (LHC) with 8 TeV center-of-mass energy. A new Support Vector Machines (SVM) High-Energy Physics interface (SVM-HINT) software is introduced to classify signal events originating from new physics processes and the SM background. SVM-HINT is enhanced with a novel statistical significance based optimization algorithm providing a state-of-the-art classification power. Monte Carlo simulations are used in the training and optimization procedure, and high signal purity search regions are determined in the search for top-squark pair production. The background event yields in each search region are predicted using a data-driven background estimation method. The results are interpreted within a simplified model assuming a top squark branching ratio of 100% to top-quark and LSP. No significant discrepancy between the data and the SM predictions has been observed. Exclusion limits were derived to constrain the mass of top squark and mass of LSP of the investigated simplified model. The sensitivity of the previous searches with the 8 TeV center-of-mass energy in the single lepton final states is extended to 675 GeV top squark mass and 225 GeV LSP mass.
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