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| Home > Publications database > Prediction of the $\text{t}\bar{\text{t}}$ and $\text{W}+\text{Jets}$ Background in a Search for New Physics with Jets and Missing Transverse Energy at CMS |
| Home > Publications database > Prediction of the $\text{t}\bar{\text{t}}$ and $\text{W}+\text{Jets}$ Background in a Search for New Physics with Jets and Missing Transverse Energy at CMS |
| Book/Report/Dissertation / PhD Thesis | PUBDB-2016-01240 |
; ;
2016
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/DESY-THESIS-2016-005
Report No.: DESY-THESIS-2016-005
Abstract: One of the primary goals of the LHC is the search for physics beyond the Standard Model (SM). Among the most studied extensions of the SM is supersymmetry (SUSY), which postulates a symmetry between fermions and bosons and requires the introduction of a SUSY partner particle for every SM particle. At the LHC the production of colored SUSY particles (squarks $\tilde{\text{q}}$ and gluinos $\tilde{\text{g}}$) can have a significant cross section, leading to distinct signatures. These particles decay to lighter new particles typically emitting quarks and gluons. Furthermore, the lightest SUSY particle is often assumed to be stable and only weakly interacting, hence it escapes the detector and leads to missing transverse energy.\\ In this thesis, a search for such new particles with proton-proton collision data recorded at the CMS experiment at $\sqrt{s}=8\ \text{TeV}$, corresponding to an integrated luminosity of $19.5 \text{fb}^{-1}$, which is performed in the final states with jets, missing transverse momentum, and no isolated muons or electrons. All SM background contributions are determined from data. A major background contribution arises from $\text{t}\bar{\text{t}}$ and $\text{W}+\text{Jets}$ events where a W boson decays into an electron or muon which is not identified in the detector, referred to as "lost-lepton". Such events contribute to the search selections if the muons and electrons are unidentified, here denoted as ``lost-leptons''. The main focus of this thesis is on the development and validation of a method to estimate the amount of lost-lepton events using a single-lepton control sample from data.\\The number of observed events are found to be consistent with the SM background expectation. Upper exclusion limits on SUSY particle masses are derived in different simplified models of $\tilde{\text{g}}$ and $\tilde{\text{q}}$ pair production. The production of light-flavor $\tilde{\text{q}}$ below a mass of 780 GeV and $\tilde{\text{g}}$ with masses below 1.1-1.2 TeV are excluded at 95\% confidence level. Furthermore, the lost-lepton prediction method is refined for the application to the new LHC data at $\sqrt{s}=13\ \text{TeV}$ , and the performance of the relevant physics object reconstruction is demonstrated using the first $42 \text{pb}^{-1}$ of $\sqrt{s}=13\ \text{TeV}$ data.
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