Measurement of the Jet Energy Scale in the CMS experiment ... - IIHE

More documents

Recommendations

Info

136 BIBLIOGRAPHY[95] A. Ealet, WW cross sections and W branching ratios,.[96] Standard Model Cross Sections for CMS at 7 TeV,https://twiki.cern.ch/twiki/bin/viewauth/CMS/StandardModelCrossSections.[97] Reference Page for Top-Quark Analyses: Samples and Cross-Sections,https://twiki.cern.ch/twiki/bin/view/CMS/CrossSections 3XSeries.[98] Electron Identification Based on Simple Cuts,https://twiki.cern.ch/twiki/bin/view/CMS/SimpleCutBasedEleID.[99] A. Rizzi, F. Palla, and G. Segneri, Track impact parameter based b-tagging withCMS, Tech. Rep. CMS-NOTE-2006-019. CERN-CMS-NOTE-2006-019, CERN,Geneva, Jan, 2006.[100] TMVA Toolkit for Multivariate Data Analysis with ROOT,http://tmva.sourceforge.net/.[101] Top Quark Analysis Framework page: Jet-Parton Association Algorithms,https://twiki.cern.ch/twiki/bin/view/CMSPublic/SWGuideTQAFLayer2#Jet Parton Asso[102] J. M. Bauer, Kinematic Fit for the Radiative Bhabha Calibration of BaBar’sElectromagnetic Calorimeter, Tech. Rep. hep-ex/0011019. SLAC-PUB-8650.UMS-HEP-2000-09, SLAC, Stanford, CA, Nov, 2000.[103] J. D’Hondt, S. Lowette, et al., Fitting of Event Topologies with ExternalKinematic Constraints in CMS, CMS Note-2006/023.[104] Reference Selection for the t¯t → e + jets Channel,https://twiki.cern.ch/twiki/bin/viewauth/CMS/TopLeptonPlusJetsRefSel el.[105] F. Bostock et al., Plans for measurement of t¯t cross section in the semileptonicelectron channel with 20 pb −1 of data at √ s of 10 TeV, CMS AN-2009/075.[106] P. Van Mulders and J. D’Hondt, Calibration of the jet energy scale using topquark events at the LHC. PhD thesis, Vrije U., Brussels & Antwerp U., Brussels& Antwerp, 2010. Presented on Jun 2010.
SummaryJets appear in the final state of many processes of interest at the Large Hadron Colliderand a precise measurement of their energies is of great importance when searching fornew physics phenomena. Since the reconstruction of the jet objects at hadron collidersis a challenging task, calibration strategies are developed to compensate for the nonperfectionof the jet energy measurements. Historically, jets at hadron colliders arecalibrated using QCD dijet events. The resolution on the jet energy measurement canbe further improved considering the physics constraints which can be imposed on anobserved top quark pair system. Due to the precise measurement of the top quarkmass at the Tevatron collider, top quarks can be used as a calibration tool to improvethe performance of the diverse analyses. Imposing the top quark and W boson massconstraints on the system containing a top quark decaying to jets, and altering the jetenergies within their uncertainties, one can obtain the residual jet energy calibrationfactors.In this thesis the method to estimate the residual jet energy corrections is appliedon the events where top quark pairs are produced in proton-proton collisions and subsequentlydecay to an isolated electron and at least four reconstructed jets and missingtransverse energy, hence pp → t¯t → W + W − b¯b → eν e q¯qb¯b processes. The leptonic sideof the event topology is mainly used to suppress the QCD multijet background eventsand the hadronic side is used for the calibration purpose. Event selection cuts areapplied to enhance the ratio of signal to background events to about S/B ≃ 2.5, whichis obtained based on a sample of simulated proton collisions corresponding to 100pb −1of integrated luminosity at a center of mass energy of 7 TeV. In order to reconstructthe topology of the hadronic decay of the top quark in e+jets t¯t events, it is requiredto assign the three jets arising from the hadronic top to the three partons. A Multi-Variate Analysis method is used to perform the association of the jets to the quarks. Inabout 17% of e+jets t¯t events, the MVA method is able to return the correct combination,where a matching between jets and partons is found. Applying an event-by-eventkinematic fitting technique with Lagrange multipliers, the masses of the W boson andof the top quark are used to constrain the e+jets t¯t events in the hadronic branch. Thekinematic fit is applied in a two-dimensional range of residual jet energy corrections(∆E l , ∆E b ). The points (∆ε l est , ∆ε b est ) minimizing the χ 2 of the fit are the estimatedresidual jet energy corrections. The precision of the method to estimate the residualjet energy corrections is limited to a systematical uncertainty of about 0.9% for lightquark jets and of about 1.0% for b quark jets. The main source of the systematicaluncertainty on the estimation of the b quark jet energy correction originates from theuncertainty on the measured top quark mass provided by the Tevatron collider.137
Page 1:
Vrije Universiteit BrusselFaculteit
Page 5 and 6:
IntroductionThe Standard Model of p
Page 7 and 8:
Chapter 1The Standard Model of Part
Page 9 and 10:
CHAPTER 1: The Standard Model of Pa
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Chapter 2The CMS experiment at the
Page 21 and 22:
CHAPTER 2: The CMS experiment at th
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Chapter 3Object ReconstructionThe e
Page 35 and 36:
CHAPTER 3: Object Reconstruction 31
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Chapter 4Reconstructing and Selecti
Page 53 and 54:
CHAPTER 4: Reconstructing and Selec
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Chapter 5Estimating of the Jet Ener
Page 73 and 74:
CHAPTER 5: Estimating of the Jet En
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90: CHAPTER 5: Estimating of the Jet En
Page 91 and 92: 2χ / ndf18.76 / 7p0 9.492e-08 ±9.
Page 131 and 132: Chapter 6ConclusionThe Standard Mod
Page 133 and 134: CHAPTER 6: Conclusion 129The method
Page 135 and 136: Bibliography[1] M. E. Peskin and D.
Page 137 and 138: BIBLIOGRAPHY 133[40] The ALICE Coll
Page 139: BIBLIOGRAPHY 135[76] The CMS Collab
show all

Measurement of the Jet Energy Scale in the CMS experiment ... - IIHE

Create successful ePaper yourself

Delete template?

Save as template?