Top quark measurements and calibration of the Soft Muon Tagger using the ATLAS detector at the Large Hadron Collider

Jacob Blanco

Research output: ThesisDoctoral Thesis

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This thesis presents top quark measurements where b-jets are identi ed by searching for “soft” muons produced within them. This method, a form of soft muon tagging, discriminates between b-jets and jets from other quark types, by using the quality of the match (χ 2 match) between the muon tracks recorded in the inner detector and muon system of the ATLAS detector. The data/MC e ciency scale factor is obtained on ATLAS data at √ s = 8 TeV using a tag and probe method on muons from J/ψ decays. The number of muons which are selected by the χ 2 match-tagger is obtained from a t to the invariant mass of the pair. A measurement of the top quark pair production in the lepton plus jets channel using the soft muon tagger on ATLAS data at √ s = 7 TeV is presented. The multijet background component was estimated using data-driven methods known as the matrix method and the ABCD method. The measured cross section is in good agreement with theoretical calculations and other measurements from ATLAS and CMS. The nal measured cross section is: σtt¯ = 165 ± 2 (stat.) ± 17 (syst.) ± 3 (lumi.) pb The viability of using the χ 2 match-based soft muon tagger in the search for boosted resonant production of tt¯pairs via the theoretical Z 0 boson is also presented. Due to the large boost in the event, the products of the top quarks merge in a collimated cone. The performance of the χ 2 match-tagger in identifying the W muon and as a b-tagger is tested. It is found that the tagger provides an additional acceptance to the W muon of 8 % over the current method known as mini-isolation. As a b-tagger the χ 2 match-tagger adds an extra 12 % more b-jets when compared to using the MV1 tagger only.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Boisvert, Veronique, Supervisor
  • Berry, Tracey, Advisor
Award date1 May 2015
Publication statusUnpublished - 2015


  • CERN
  • LHC
  • Top Physics
  • HEP

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