Measurement of the top anti-top quark pair production cross section in the dilepton decay channel using Lepton+Track selection in 7 TeV p − p collisions with L = 698 PB−1

Khandanyan, Hovhannes

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https://hdl.handle.net/2142/30962 Copy

Description

Title

Measurement of the top anti-top quark pair production cross section in the dilepton decay channel using Lepton+Track selection in 7 TeV p − p collisions with L = 698 PB−1

Author(s)

Khandanyan, Hovhannes

Issue Date

2012-05-22T00:18:41Z

Director of Research (if dissertation) or Advisor (if thesis)

Errede, Steven M.

Doctoral Committee Chair(s)

Wiss, J.E.

Committee Member(s)

• Errede, Steven M.
• Stack, John D.
• Cooper, S. Lance

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Cross Section
• Cross Section Measurement
• Lepton+Track
• Track-Lepton
• ATLAS Cross Section
• ATLAS Thesis
• UIUC Thesis
• UIUC ATLAS
• Hovhannes
• Khandanyan
• Hovhannes Khandanyan Thesis
• Hovhannes Khandanyan Dissertation
• University of Illinois Champaign-Urbana (UIUC)

Abstract

We present measurements of the t¯t production cross section obtained using the ATLAS detector at the LHC with pp collisions at √s = 7 TeV in dilepton final states, from a data sample of L=698 pb−1 taken in 2011. For dilepton pair selection we have used a ‘Lepton+Track’ approach, where selection requirements on one lepton leg are reduced to a requirement of only a high quality Inner Detector track. This proce- dure, while allowing more background in the selected sample, enhances the sensitivity to τ-leptonic decays of the W± and increases the t¯t acceptance by 20% over the conventional dilepton analysis (where each lepton is identified as an electron or muon). Two modes of the l+track analysis were studied: the inclu- sive and the exclusive mode. The measured t¯t cross sections in the inclusive eTL and μTL channels are 182.9±9.3 (stat.)+21.9 −16.7 (syst.)+8.2 −7.3 (lum.) pb and 171.0±8.5 (stat.)+20.6 −17.5 (syst.)+7.8 −7.0 (lum.) pb, respectively. The inclusive eTL and μTL combined t¯t cross section is 177.4±6.3 (stat.)+18.4 −15.2 (syst.)±7.6 (lum.) pb. The mea- sured t¯t cross sections in the exclusive eTL and μTL channels are 160.8 ±22.6 (syst.)+45.1 −33.1 (syst.)+8.3 −6.8 (lum.) pb and 168.3 ± 23.9 (syst.)+45.8 −39.0 (syst.)+9.0 −7.5 (lum.) pb, respectively. The exclusive eTL and μTL combined t¯t cross section is 164.5 ± 16.4 (syst.)+39.0 −30.5 (syst.)+8.6 −7.1 (lum.) pb. These t¯t cross section measurements are consistent with each other and are in good agreement with the Standard Model prediction of 164.6+11.5 −15.8 pb.

Graduation Semester

2012-05

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http://hdl.handle.net/2142/30962

Copyright and License Information

Copyright 2012 by Hovhannes Khandanyan. All rights reserved.

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