Search for the Standard Model Higgs boson produced in association with a pair of top quarks and decaying into a bb-pair in the single lepton channel at sqrt{s} = 8 TeV with the ATLAS experiment at the LHC

by Leonid Serkin
Doctoral thesis
Date of Examination:2016-08-03
Date of issue:2016-08-18
Advisor:Prof. Dr. Arnulf Quadt
Referee:Prof. Dr. Arnulf Quadt
Referee:Prof. Dr. Stan Lai
Persistent Address: http://dx.doi.org/10.53846/goediss-5807

 

 

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Abstract

English

This thesis focuses on the search for the Standard Model Higgs boson produced in association with a pair of top quarks, ttH, using 20.3 fb-1 of pp collision data at sqrt{s} = 8 TeV, collected with the ATLAS detector at the Large Hadron Collider during 2012. The search is designed for the H -> bb decay mode and is performed in the single lepton channel, characterised by an isolated electron or muon, missing transverse energy and at least four jets. In order to improve the sensitivity of the search, events are categorised according to their jet and b-tagged jet multiplicities into nine analysis regions. The discrimination between signal and background, the latter being dominated by tt+jets production, is obtained by employing neural networks in signal-enriched regions. No significant excess of events above the background expectation is found and an observed (expected) upper limit of 3.6 (2.6) times the Standard Model cross section is obtained at 95% confidence level. The search in the single lepton channel significantly contributes to the combination of various ttH searches carried out by ATLAS Collaboration at sqrt{s} = 7 and 8 TeV, yielding a measured (expected) significance for the observation of the ttH production process of 2.3 sigma (1.5 sigma).
Keywords: Higgs boson, top quark, ttH, tt+Higgs, ATLAS, LHC
 
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