publication . Doctoral thesis . Other literature type . 2015

Search for Supersymmetry in Final States with a Single Lepton, B-Quark Jets, and Missing Transverse Energy at the CMS Experiment

Pietsch, Niklas Andreas;
Open Access English
  • Published: 01 Jan 2015
  • Country: Germany
Abstract
Supersymmetry constitutes an attractive extension of the Standard Model of parti- cle physics. It provides a natural Dark Matter candidate and is able to resolve the hierarchy problem. If Supersymmetry is a natural solution of the hierarchy problem, the supersymmetric partner particles of the top and the bottom quark may be copi- ously produced in proton-proton collisions at the Large Hadron Collider, resulting in nal states with isolated leptons, jets, some of which originate from a bottom quark, and missing transverse energy. In this thesis, the rst search for Supersymmetry in events with a single lepton, bottom quark-jets, and missing transverse energy at the...
Subjects
arXiv: High Energy Physics::PhenomenologyHigh Energy Physics::Experiment
free text keywords: Dissertation, Detectors and Experimental Techniques
Related Organizations
Download fromView all 2 versions
CERN Document Server
Other literature type . 2015
69 references, page 1 of 5

2. Theoretical Framework 5 2.1. The Standard Model of Particle Physics . . . . . . . . . . . . . . . . 6 2.1.1. Electroweak Interaction . . . . . . . . . . . . . . . . . . . . . 6 2.1.2. Electroweak Symmetry Breaking . . . . . . . . . . . . . . . . 11 2.1.3. Strong Interaction . . . . . . . . . . . . . . . . . . . . . . . . 15 2.1.4. Perturbation Theory and Renormalization . . . . . . . . . . . 18 2.1.5. Shortcomings of the Standard Model . . . . . . . . . . . . . . 20 2.2. Supersymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.2.1. Minimal Supersymmetric Standard Model . . . . . . . . . . . 23 2.2.2. Constrained Minimal Supersymmetric Standard Model . . . . 28 2.2.3. Phenomenology of Light Top and Bottom Squarks . . . . . . . 29 2.2.4. Simpli ed Models . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.3. Other Extensions of the Standard Model . . . . . . . . . . . . . . . . 39 2.3.1. Extra Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.3.2. Grand Uni ed Theories . . . . . . . . . . . . . . . . . . . . . . 41 2.3.3. Fourth Generation of Quarks . . . . . . . . . . . . . . . . . . 41

3. Experimental Setup 43 3.1. The Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . . . 43 3.2. The CMS Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2.1. Tracking System . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.2.2. Electromagnetic Calorimeter . . . . . . . . . . . . . . . . . . . 47 3.2.3. Hadronic Calorimeter . . . . . . . . . . . . . . . . . . . . . . . 48 3.2.4. Muon System . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.2.5. Trigger and Data Acquisition . . . . . . . . . . . . . . . . . . 51 3.2.6. Computing Model and Analysis Tools . . . . . . . . . . . . . . 51 4.1.5. Hadronization and Decay . . . . . . . . . . . . . . . . . . . . . 57 4.1.6. Pile-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.1.7. Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . 58 4.2. Event Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.3. Simulated Event Samples . . . . . . . . . . . . . . . . . . . . . . . . . 60 4.3.1. Simulated Signal Samples . . . . . . . . . . . . . . . . . . . . 60 4.3.2. Simulated Background Samples . . . . . . . . . . . . . . . . . 62

5. Object Reconstruction 67 5.1. Primary Vertex Reconstruction . . . . . . . . . . . . . . . . . . . . . 68 5.2. Muon Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 5.3. Electron Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . 71 5.4. Particle-Flow Approach . . . . . . . . . . . . . . . . . . . . . . . . . . 72 5.5. Jet Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 5.6. B-Jet Identi cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

6. Event Selection 77 6.1. Trigger Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.2. Preselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.2.1. Primary Vertex Selection and Event Cleaning . . . . . . . . . 81 6.2.2. Lepton Selection . . . . . . . . . . . . . . . . . . . . . . . . . 82 6.2.3. HT and E=T Selection . . . . . . . . . . . . . . . . . . . . . . . 82 6.2.4. Control Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 6.3. Jet Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.4. B-Jet Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 6.5. Selected Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

7. Background Prediction From Data 105 7.1. Factorization Method with HT and YMET . . . . . . . . . . . . . . . . 107 7.1.1. Factorization Ansatz . . . . . . . . . . . . . . . . . . . . . . . 110 7.1.2. Signal and Control Regions . . . . . . . . . . . . . . . . . . . 110 7.2. Background from Semileptonic tt Decays with a Muon or Electron . . 115 7.2.1. Correlation between HT and pT . . . . . . . . . . . . . . . . . 118 7.2.2. Correlation between HT and E=T pT . . . . . . . . . . . . . . 122 7.2.3. In uence of the Event Selection . . . . . . . . . . . . . . . . . 125 7.2.4. In uence of the Control and Signal Region De nition . . . . . 130 7.3. Background From Other Standard Model Processes . . . . . . . . . . 132 7.3.1. Semileptonic tt Decays with a Tau in the Final State . . . . . 133 7.3.2. Dileptonic tt Decays . . . . . . . . . . . . . . . . . . . . . . . 134 7.3.3. W+Jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 7.3.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

8. Systematic Uncertainties 139 8.1. Theoretical Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . 140 8.1.1. Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 8.1.2. Factorization and Renormalization Scales . . . . . . . . . . . . 140 8.1.3. Matrix Element-Parton Shower Matching . . . . . . . . . . . . 141 8.2. Cross Check in the 0-b-tag Channel . . . . . . . . . . . . . . . . . . . 142 8.3. Experimental Uncertainties . . . . . . . . . . . . . . . . . . . . . . . 143 8.3.1. Lepton Energy Scale . . . . . . . . . . . . . . . . . . . . . . . 144 8.3.2. Jet Energy Scale . . . . . . . . . . . . . . . . . . . . . . . . . 144 8.3.3. Jet Energy Resolution . . . . . . . . . . . . . . . . . . . . . . 145 8.3.4. Unclustered Energy Scale . . . . . . . . . . . . . . . . . . . . 145 8.3.5. Trigger E ciency . . . . . . . . . . . . . . . . . . . . . . . . . 145 8.3.6. Lepton Reconstruction E ciency . . . . . . . . . . . . . . . . 146 8.3.7. B-Jet Identi cation E ciency . . . . . . . . . . . . . . . . . . 146 8.3.8. Pile-Up Simulation . . . . . . . . . . . . . . . . . . . . . . . . 146 8.3.9. Integrated Luminosity . . . . . . . . . . . . . . . . . . . . . . 146 8.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

[2] W. V. O. Quine, \Two dogmas of empiricism", Phil.Rev. 60 (1951) 20{43.

[3] E. Noether, \Invarianten beliebiger Di erentialausdrucke", Gott. Nachr. (1918) 37{44.

[4] R. Haag, J. T. Lopuszanski, and M. Sohnius, \All Possible Generators of Supersymmetries of the s Matrix", Nucl.Phys. B88 (1975) 257. doi:10.1016/0550-3213(75)90279-5. [OpenAIRE]

[5] M. Papucci, J. T. Ruderman, and A. Weiler, \Natural SUSY Endures", JHEP 1209 (2012) 035, arXiv:1110.6926. doi:10.1007/JHEP09(2012)035. [OpenAIRE]

[6] Planck Collaboration Collaboration, \Planck 2013 results. I. Overview of products and scienti c results", arXiv:1303.5062. doi:10.1051/0004-6361/201321529.

[7] CMS Collaboration, \Search for supersymmetry in nal states with a single lepton, b-quark jets, and missing transverse energy in proton-proton collisions at ps = 7 TeV", Phys.Rev. D87 (2013), no. 5, 052006, arXiv:1211.3143. doi:10.1103/PhysRevD.87.052006.

[8] N. Pietsch, J. Reuter, K. Sakurai et al., \Extracting Gluino Endpoints with Event Topology Patterns", JHEP 1207 (2012) 148, arXiv:1206.2146. doi:10.1007/JHEP07(2012)148.

[9] V. D. Barger and R. J. N. Phillips, \Collider Physics". Frontiers in Physics. Westview Press, Boulder, Colorado, 1996. ISBN 978-0201149456.

[10] D. Gri ths, \Introduction to elementary particles". Wiley-VCH Verlag Gmbh & Co KGaA, Weinheim, 1988. ISBN 978-3-527-40601-2.

69 references, page 1 of 5
Related research
Abstract
Supersymmetry constitutes an attractive extension of the Standard Model of parti- cle physics. It provides a natural Dark Matter candidate and is able to resolve the hierarchy problem. If Supersymmetry is a natural solution of the hierarchy problem, the supersymmetric partner particles of the top and the bottom quark may be copi- ously produced in proton-proton collisions at the Large Hadron Collider, resulting in nal states with isolated leptons, jets, some of which originate from a bottom quark, and missing transverse energy. In this thesis, the rst search for Supersymmetry in events with a single lepton, bottom quark-jets, and missing transverse energy at the...
Subjects
arXiv: High Energy Physics::PhenomenologyHigh Energy Physics::Experiment
free text keywords: Dissertation, Detectors and Experimental Techniques
Related Organizations
Download fromView all 2 versions
CERN Document Server
Other literature type . 2015
69 references, page 1 of 5

2. Theoretical Framework 5 2.1. The Standard Model of Particle Physics . . . . . . . . . . . . . . . . 6 2.1.1. Electroweak Interaction . . . . . . . . . . . . . . . . . . . . . 6 2.1.2. Electroweak Symmetry Breaking . . . . . . . . . . . . . . . . 11 2.1.3. Strong Interaction . . . . . . . . . . . . . . . . . . . . . . . . 15 2.1.4. Perturbation Theory and Renormalization . . . . . . . . . . . 18 2.1.5. Shortcomings of the Standard Model . . . . . . . . . . . . . . 20 2.2. Supersymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.2.1. Minimal Supersymmetric Standard Model . . . . . . . . . . . 23 2.2.2. Constrained Minimal Supersymmetric Standard Model . . . . 28 2.2.3. Phenomenology of Light Top and Bottom Squarks . . . . . . . 29 2.2.4. Simpli ed Models . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.3. Other Extensions of the Standard Model . . . . . . . . . . . . . . . . 39 2.3.1. Extra Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.3.2. Grand Uni ed Theories . . . . . . . . . . . . . . . . . . . . . . 41 2.3.3. Fourth Generation of Quarks . . . . . . . . . . . . . . . . . . 41

3. Experimental Setup 43 3.1. The Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . . . 43 3.2. The CMS Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2.1. Tracking System . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.2.2. Electromagnetic Calorimeter . . . . . . . . . . . . . . . . . . . 47 3.2.3. Hadronic Calorimeter . . . . . . . . . . . . . . . . . . . . . . . 48 3.2.4. Muon System . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.2.5. Trigger and Data Acquisition . . . . . . . . . . . . . . . . . . 51 3.2.6. Computing Model and Analysis Tools . . . . . . . . . . . . . . 51 4.1.5. Hadronization and Decay . . . . . . . . . . . . . . . . . . . . . 57 4.1.6. Pile-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.1.7. Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . 58 4.2. Event Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.3. Simulated Event Samples . . . . . . . . . . . . . . . . . . . . . . . . . 60 4.3.1. Simulated Signal Samples . . . . . . . . . . . . . . . . . . . . 60 4.3.2. Simulated Background Samples . . . . . . . . . . . . . . . . . 62

5. Object Reconstruction 67 5.1. Primary Vertex Reconstruction . . . . . . . . . . . . . . . . . . . . . 68 5.2. Muon Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 5.3. Electron Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . 71 5.4. Particle-Flow Approach . . . . . . . . . . . . . . . . . . . . . . . . . . 72 5.5. Jet Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 5.6. B-Jet Identi cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

6. Event Selection 77 6.1. Trigger Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.2. Preselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 6.2.1. Primary Vertex Selection and Event Cleaning . . . . . . . . . 81 6.2.2. Lepton Selection . . . . . . . . . . . . . . . . . . . . . . . . . 82 6.2.3. HT and E=T Selection . . . . . . . . . . . . . . . . . . . . . . . 82 6.2.4. Control Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 6.3. Jet Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.4. B-Jet Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 6.5. Selected Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

7. Background Prediction From Data 105 7.1. Factorization Method with HT and YMET . . . . . . . . . . . . . . . . 107 7.1.1. Factorization Ansatz . . . . . . . . . . . . . . . . . . . . . . . 110 7.1.2. Signal and Control Regions . . . . . . . . . . . . . . . . . . . 110 7.2. Background from Semileptonic tt Decays with a Muon or Electron . . 115 7.2.1. Correlation between HT and pT . . . . . . . . . . . . . . . . . 118 7.2.2. Correlation between HT and E=T pT . . . . . . . . . . . . . . 122 7.2.3. In uence of the Event Selection . . . . . . . . . . . . . . . . . 125 7.2.4. In uence of the Control and Signal Region De nition . . . . . 130 7.3. Background From Other Standard Model Processes . . . . . . . . . . 132 7.3.1. Semileptonic tt Decays with a Tau in the Final State . . . . . 133 7.3.2. Dileptonic tt Decays . . . . . . . . . . . . . . . . . . . . . . . 134 7.3.3. W+Jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 7.3.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

8. Systematic Uncertainties 139 8.1. Theoretical Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . 140 8.1.1. Cross Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 8.1.2. Factorization and Renormalization Scales . . . . . . . . . . . . 140 8.1.3. Matrix Element-Parton Shower Matching . . . . . . . . . . . . 141 8.2. Cross Check in the 0-b-tag Channel . . . . . . . . . . . . . . . . . . . 142 8.3. Experimental Uncertainties . . . . . . . . . . . . . . . . . . . . . . . 143 8.3.1. Lepton Energy Scale . . . . . . . . . . . . . . . . . . . . . . . 144 8.3.2. Jet Energy Scale . . . . . . . . . . . . . . . . . . . . . . . . . 144 8.3.3. Jet Energy Resolution . . . . . . . . . . . . . . . . . . . . . . 145 8.3.4. Unclustered Energy Scale . . . . . . . . . . . . . . . . . . . . 145 8.3.5. Trigger E ciency . . . . . . . . . . . . . . . . . . . . . . . . . 145 8.3.6. Lepton Reconstruction E ciency . . . . . . . . . . . . . . . . 146 8.3.7. B-Jet Identi cation E ciency . . . . . . . . . . . . . . . . . . 146 8.3.8. Pile-Up Simulation . . . . . . . . . . . . . . . . . . . . . . . . 146 8.3.9. Integrated Luminosity . . . . . . . . . . . . . . . . . . . . . . 146 8.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

[2] W. V. O. Quine, \Two dogmas of empiricism", Phil.Rev. 60 (1951) 20{43.

[3] E. Noether, \Invarianten beliebiger Di erentialausdrucke", Gott. Nachr. (1918) 37{44.

[4] R. Haag, J. T. Lopuszanski, and M. Sohnius, \All Possible Generators of Supersymmetries of the s Matrix", Nucl.Phys. B88 (1975) 257. doi:10.1016/0550-3213(75)90279-5. [OpenAIRE]

[5] M. Papucci, J. T. Ruderman, and A. Weiler, \Natural SUSY Endures", JHEP 1209 (2012) 035, arXiv:1110.6926. doi:10.1007/JHEP09(2012)035. [OpenAIRE]

[6] Planck Collaboration Collaboration, \Planck 2013 results. I. Overview of products and scienti c results", arXiv:1303.5062. doi:10.1051/0004-6361/201321529.

[7] CMS Collaboration, \Search for supersymmetry in nal states with a single lepton, b-quark jets, and missing transverse energy in proton-proton collisions at ps = 7 TeV", Phys.Rev. D87 (2013), no. 5, 052006, arXiv:1211.3143. doi:10.1103/PhysRevD.87.052006.

[8] N. Pietsch, J. Reuter, K. Sakurai et al., \Extracting Gluino Endpoints with Event Topology Patterns", JHEP 1207 (2012) 148, arXiv:1206.2146. doi:10.1007/JHEP07(2012)148.

[9] V. D. Barger and R. J. N. Phillips, \Collider Physics". Frontiers in Physics. Westview Press, Boulder, Colorado, 1996. ISBN 978-0201149456.

[10] D. Gri ths, \Introduction to elementary particles". Wiley-VCH Verlag Gmbh & Co KGaA, Weinheim, 1988. ISBN 978-3-527-40601-2.

69 references, page 1 of 5
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