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Search for Heavy Resonances Decaying to Top Quark Pairs in the Boosted All-Hadronic Decay Channel

Many theories of physics beyond the Standard Model predict the existence of TeV-scale resonances that decay to top quark pairs. This thesis presents a search for such resonances produced in proton-proton collisions at a centre-of-mass energy of 7 TeV at the CERN Large Hadron Collider with 4.7 fb−1 of data collected by the ATLAS detector in 2011. The search is performed in the channel where both top quarks decay hadronically and emerge in highly boosted states, and the collimated decay products of each boosted top quark are reconstructed as a single large jet (a “top quark jet”). A tagging technique based on the distinctive masses and substructures of these top quark jets is used to distinguish them from light quark and gluon jets. The data are found to be consistent with Standard Model predictions, and 95% credibility level upper limits are set on the cross section times branching ratio for leptophobic Z' bosons in a Topcolour model and Kaluza-Klein gluons as predicted by the bulk Randall-Sundrum model. These limits exclude Kaluza-Klein gluons with masses between 1.02 TeV and 1.62 TeV. The substructure of light quark and gluon jets, which form the dominant background to hadronically decaying boosted top quarks, is studied in an auxiliary measurement using 35 pb−1 of data collected by ATLAS during the 2010 run period. The observed substructure of these jets are found to be in good agreement with theoretical predictions.

Identiferoai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/43946
Date05 March 2014
CreatorsFarooque, Trisha
ContributorsSinervo, Pekka
Source SetsUniversity of Toronto
Languageen_ca
Detected LanguageEnglish
TypeThesis

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