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Searching for physics beyond the Standard Model in ATLAS with the third generation quarks

ATLAS (A Toroidal LHC Apparatus) is one of the general-purpose detectors at the CERN's Large Hadron Collider (LHC), designed to study proton-proton collisions at a center of mass energy of 14 TeV. This PhD thesis starts with a performance measurement of the Inner Detector, followed by the measu...

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Autor principal: Favareto, Andrea
Lenguaje:eng
Publicado: 2013
Materias:
Acceso en línea:http://cds.cern.ch/record/1517520
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author Favareto, Andrea
author_facet Favareto, Andrea
author_sort Favareto, Andrea
collection CERN
description ATLAS (A Toroidal LHC Apparatus) is one of the general-purpose detectors at the CERN's Large Hadron Collider (LHC), designed to study proton-proton collisions at a center of mass energy of 14 TeV. This PhD thesis starts with a performance measurement of the Inner Detector, followed by the measurement of an interesting Standard Model process on early data in which tracking and b-tagging play a fundamental role. Finally a search for new physics on the high integrated luminosity sample is presented. It includes a detailed measurement of the tracks impact parameter resolution as a function on the pseudorapidity η, the pT and the number of hits and shared hits in the silicon detectors of the tracks. The transverse impact parameter is measured to be ~10 μm for high pT tracks (pT>20 GeV) in a central η region with one hit in the innermost pixel layer (b-layer) and without shared hits with other tracks in the silicon detectors. Two measurements are then presented, that profit of this excellent resolution and the related b-tagging performance. The first measurement of the charge asymmetry in the production of top quark pairs in the semileptonic decay channel. A dataset corresponding to an integrated luminosity of 1.04 fb-1, obtained at a center-of-mass energy of √s=7 TeV is used. The charge asymmetry is determined using the differential distribution of the reconstructed observable|yt|-|yT|, where yt and yT denote the top and antitop quark rapidities, respectively. The total charge asymmetry after unfolding is measured to be -0.019 ± 0.028 (stat.) ± 0.024 (syst.) in agreement with the Standard Model prediction of (0.60±0.03)%. Finally, the results of a search for direct pair production of supersymmetric partners of the top quark in 4.7 fb-1 and 13.0 fb-1 of integrated luminosity from proton-proton collisions respectively collected at 7 TeV in 2011 and 8 TeV in 2012 are reported. Scalar top quarks decaying into a b-quark and a superymmetric chargino are searched for in events with two leptons in the final state. This events have a final state topology similar that of top-antitop events and this analysis builds up on the experience that I gained with the top-antitop charge asymmetry measurement. No excess above the Standard Model expectation is observed. A scalar top with mass between 150 and 450 GeV is excluded at 95% CL for a chargino approximately degenerate with the scalar top and a massless ligthest neutralino.
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spelling cern-15175202019-09-30T06:29:59Zhttp://cds.cern.ch/record/1517520engFavareto, AndreaSearching for physics beyond the Standard Model in ATLAS with the third generation quarksParticle Physics - ExperimentATLAS (A Toroidal LHC Apparatus) is one of the general-purpose detectors at the CERN's Large Hadron Collider (LHC), designed to study proton-proton collisions at a center of mass energy of 14 TeV. This PhD thesis starts with a performance measurement of the Inner Detector, followed by the measurement of an interesting Standard Model process on early data in which tracking and b-tagging play a fundamental role. Finally a search for new physics on the high integrated luminosity sample is presented. It includes a detailed measurement of the tracks impact parameter resolution as a function on the pseudorapidity η, the pT and the number of hits and shared hits in the silicon detectors of the tracks. The transverse impact parameter is measured to be ~10 μm for high pT tracks (pT>20 GeV) in a central η region with one hit in the innermost pixel layer (b-layer) and without shared hits with other tracks in the silicon detectors. Two measurements are then presented, that profit of this excellent resolution and the related b-tagging performance. The first measurement of the charge asymmetry in the production of top quark pairs in the semileptonic decay channel. A dataset corresponding to an integrated luminosity of 1.04 fb-1, obtained at a center-of-mass energy of √s=7 TeV is used. The charge asymmetry is determined using the differential distribution of the reconstructed observable|yt|-|yT|, where yt and yT denote the top and antitop quark rapidities, respectively. The total charge asymmetry after unfolding is measured to be -0.019 ± 0.028 (stat.) ± 0.024 (syst.) in agreement with the Standard Model prediction of (0.60±0.03)%. Finally, the results of a search for direct pair production of supersymmetric partners of the top quark in 4.7 fb-1 and 13.0 fb-1 of integrated luminosity from proton-proton collisions respectively collected at 7 TeV in 2011 and 8 TeV in 2012 are reported. Scalar top quarks decaying into a b-quark and a superymmetric chargino are searched for in events with two leptons in the final state. This events have a final state topology similar that of top-antitop events and this analysis builds up on the experience that I gained with the top-antitop charge asymmetry measurement. No excess above the Standard Model expectation is observed. A scalar top with mass between 150 and 450 GeV is excluded at 95% CL for a chargino approximately degenerate with the scalar top and a massless ligthest neutralino.CERN-THESIS-2013-011oai:cds.cern.ch:15175202013-02-20T13:18:53Z
spellingShingle Particle Physics - Experiment
Favareto, Andrea
Searching for physics beyond the Standard Model in ATLAS with the third generation quarks
title Searching for physics beyond the Standard Model in ATLAS with the third generation quarks
title_full Searching for physics beyond the Standard Model in ATLAS with the third generation quarks
title_fullStr Searching for physics beyond the Standard Model in ATLAS with the third generation quarks
title_full_unstemmed Searching for physics beyond the Standard Model in ATLAS with the third generation quarks
title_short Searching for physics beyond the Standard Model in ATLAS with the third generation quarks
title_sort searching for physics beyond the standard model in atlas with the third generation quarks
topic Particle Physics - Experiment
url http://cds.cern.ch/record/1517520
work_keys_str_mv AT favaretoandrea searchingforphysicsbeyondthestandardmodelinatlaswiththethirdgenerationquarks