Development of a new Soft Muon Tagger for the Identification of b quarks, applied to a Top Quark Pair Production Cross Section Measurement, using the ATLAS Detector at CERN.

Matthew Rose

Research output: ThesisDoctoral Thesis

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This thesis presents a study of a method for identifying b-jets by searching for “soft” muons produced within them. This method, a so-called Soft Muon Tagger, uses the quality of the match (Χ2match) between tracks left in the inner detector and the muon systems within the ATLAS detector to discriminate between muons within hadronic jets produced by the decay of b quarks, and those within light flavour jets.
The complete characteristics of the tagger are investigated in a detailed study on simulated data. The scale factors between the efficiency of the tagger in simulated and collision data, dependent on the kinematics of the tagged muon, are found using J/Ψ decays. These are used in a measurement of the top quark pair production cross section in collision data.
The measurement is performed on data taken during the 2011 run of the LHC, specifically in the lepton+jets top-antitop quark decay channel. A summary of this measurement is presented, and is found to be compatible with theoretical predictions for the cross section at a centre of mass energy of √s = 7 TeV, and with published ATLAS and CMS measurements using b-tagging in the lepton+jets channel. The measured cross section is:

σtt ̄ = 165 ± 2(stat.) ± 17(syst.) ± 3(lumi.) pb

The Χ2match-based soft muon tagger contributes a small b-tagging systematic uncertainty to the cross section measurement compared to measurements performed using lifetime based b-taggers, and has a good signal to background ratio.

Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Boisvert, Veronique, Supervisor
Award date1 Mar 2013
Publication statusUnpublished - 2013

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