Search for pair production of a heavy quark decaying into top quark and photon in semi-leptonic channel with the CMS detector in the LHC

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2014
Aşılar, Ece
In this thesis, a search for a pair produced excited quark, $t^*$, which decays exclusively to a top quark and a photon, is performed by considering semi-leptonic decay channel. This entails that there are two isolated photons, at least 4 well-reconstructed jets and one lepton, which can be either a single isolated muon or electron, in the final state. Moreover, the $\chi^{2}$ sorting method and matrix method is presented to reconstruct signal and to determine fake rate of photons coming from leptons and jets, for background reconstruction, respectively. Tag and Probe method and QCD-enriched samples are also implied to make use of matrix method. In this study, proton-proton collision data collected by CMS at 8 TeV corresponding to an integrated luminosity of 19.6${fb}^{-1}$ is investigated. Analysis is performed in a model independent way while a heavy spin-3/2 excitation of a heavy spin-1/2 quark indicated by ”Rarita-Schwinger” vector spinor Lagrangian is the most favorable choice among other beyond the standard models. As a result of this study, no significant excess is observed over expectations and a lower limit is set on a t* quark mass of 969 ${GeV/c}^{2}$ at 95$\%$ confidence level.

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Citation Formats
E. Aşılar, “Search for pair production of a heavy quark decaying into top quark and photon in semi-leptonic channel with the CMS detector in the LHC,” M.S. - Master of Science, Middle East Technical University, 2014.