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

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42 CHAPTER 3: Object ReconstructionFigure 3.10: The jet response after applying L2 and L3 corrections for a particularp GenJetT bin specified in the plot. The width of the fitted function is used to extract thejet energy resolutions.dijet events. The parameter A, which is called “Asymmetry”, is used to derivethe jet resolutions and defined to beA = (pjet1 T(p jet1T− p jet2T)+ p jet2T) ,where p jet1Tand p jet2Tare the transverse momenta of the two leading jets in eachQCD dijet event. The variance σ A can be measured and simply written asσ 2 A = | ∂A∂p jet1T| 2 σ 2 p jet1T+ |∂A∂p jet2T| 2 σ 2 .p jet2TUsing the idea of the momentum conservation in the transverse plane of the dijetevents, one can define p T ≡ p jet1T= p jet2T. The two leading jets are further requiredto be in the same η region, so that any dependency on the resolution parametersoriginating from the differences in the pseudorapidity regions is removed and onecan assume that σ pT ≡ σp jet1T= σp jet2T. Hence the fractional jet p T resolution canbe obtained from the width of th the Asymmetry parameter in the following way(σ pTp T)=√2σA .The resolutions derived from the Asymmetry method are only valid in the limitof exactly two jets in the QCD dijet events. In the case when other jets arepresent, the assumption of the equality of the transverse momenta of the twoleading jets is no longer valid. Hence in order to eliminate the radiated jetswhich spoil the assumption of p T -balancing for the two leading jets, a cut on thetransverse momentum of the third leading jet is applied, p jet3Tthe resolution values are calculated for different threshold cuts in bins of p avrT =
CHAPTER 3: Object Reconstruction 43(p jet1T+p jet2T ). As an example, the distribution of the Asymmetry variable for the2calorimeter jets with 125 inFigure 3.11.Figure 3.11: The distribution of the Asymmetry variable for calorimeter jets with125 ing jet is required to have a p Tless than 15 GeV [76].The Asymmetry distributions for various threshold cuts on the p jet3Tare fitted witha Gaussian. The jet resolutions for each bin of p avrT can then be plotted as a functionof p cutT and fitted with a line. The true jet resolution value is obtaind by extrapolatingthe fitted line to p cutT = 0 which corresponds to a QCD event with exactly two jets.For the same p avrT as the one shown in Figure 3.11, the corresponding jet resolution isshown in Figure 3.12.Figure 3.12: The fractional energy resolution as a function of the p jet3Tthreshold in thesame range of p avrT and η as Figure 3.11 derived from Asymmetry method [76].
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 19 and 20: Chapter 2The CMS experiment at the
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Page 33 and 34: Chapter 3Object ReconstructionThe e
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Page 51 and 52: Chapter 4Reconstructing and Selecti
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Page 71 and 72: Chapter 5Estimating of the Jet Ener
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CHAPTER 5: Estimating of the Jet En
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Chapter 6ConclusionThe Standard Mod
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CHAPTER 6: Conclusion 129The method
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Bibliography[1] M. E. Peskin and D.
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BIBLIOGRAPHY 133[40] The ALICE Coll
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BIBLIOGRAPHY 135[76] The CMS Collab
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SummaryJets appear in the final sta
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Measurement of the Jet Energy Scale in the CMS experiment ... - IIHE

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