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

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62 CHAPTER 4: Reconstructing and Selecting Physics Event#Events410310tt+jets semi-ele (1022.1 entries)tt+jets other (310.1 entries)t+jets, (all channels) (149.1 entries)Z+jets (1045.4 entries)W+jets (5314.5 entries)Multi-jets (12144.0 entries)210101-110-0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5Nr. of Loose MuonsFigure 4.13: Muon multiplicity per event which passed the Second Electron Veto cut.At Least Four JetsAt the pre-selection step, all events are required to have at least four reconstructed jetsin their final states. By tightening the thresholds on the jet kinematics and also by applyingsome identification criteria, the probability of selecting the four jets originatingfrom the quarks coming out of the hard scattering process becomes higher. The eventis required to have at least four selected jets with p T greater than 30GeV. Also jets,in order to be labeled as selected, are asked to pass identification cuts that are brieflydescribed below.• f EM which is called the electromagnetic energy fraction and is defined as thefraction of the jet energy measured in the ECAL. This parameter is useful indifferentiating between electrons and jets since jets with a high value of f EMprobably are electrons with energy deposits also used in the jet reconstructionalgorithm. The upper limit of this variable is set to be 0.9. Also in order tosuppress those jets which are actually pure electronic noise, a lower limit equalto 0.05 is put on this parameter.• n90Hits is defined as the minimal number of reconstructed hits containing 90%of the jet energy and is another observable that is used for the jet identification.The selected jets are required to have a n90Hits variable exceeding 4.• f HPD is defined as the fraction of energy in the hottest HPD readout. The selectedjets are asked to fulfill f HPD < 0.98.The distributions of the various identification variables of all reconstructed jets forthose events that already passed the Muon Veto cut, are shown in Figure 4.14.Looking at the distribution of the electromagnetic energy fraction, there is a clearpeak at ∼1 representing the electrons which are re-reconstructed as jets. Another plotthat shows the jet collection includes electrons and therefore needs to be cleaned, isthe distance between the selected electron and the closest jet among all reconstructed
CHAPTER 4: Reconstructing and Selecting Physics Event 63#Events410310210tt+jets semi-ele (5507.8 entries)tt+jets other (1102.6 entries)t+jets, (all channels) (669.4 entries)Z+jets (4506.7 entries)W+jets (22945.5 entries)Multi-jets (52361.7 entries)#Events310210101011-110-1100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Jets EMF0 10 20 30 40 50Jets n90Hits#Events410310210101-1100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Jets fHPDFigure 4.14: Jet identification variables of all reconstructed jets for the events whichpass the Muon Veto cut.jets and is shown in the left plot of Figure 5.26. Hence an extra criterion is appliedon each selected jet requiring it not to be located very close to the selected electron.All selected jets are asked to be reconstructed in a ∆R = √ (∆η) 2 + (∆φ) 2 cone of 0.3from the selected electron. For comparison, the same plot of the distance between theselected electron and the closest jet after cleaning is also shown in the right plot ofFigure 5.26.#Events410310210tt+jets semi-ele (1019.4 entries)tt+jets other (221.7 entries)t+jets, (all channels) (146.0 entries)Z+jets (1039.5 entries)W+jets (5308.6 entries)Multi-jets (12129.0 entries)#Events210101011-110-1100 0.5 1 1.5 2 2.5 3 3.5 4Electron Minimal ∆R(ele, jet)0 0.5 1 1.5 2 2.5 3 3.5 4Electron Minimal ∆R(ele, jet)Figure 4.15: Minimum ∆R distance between selected electron and the closest reconstructedjet before (left) and after (right) cleaning. Left plot is filled for the eventspassing the Muon Veto cut while the events with at least four selected jets populatethe right plot.
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Vrije Universiteit BrusselFaculteit
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IntroductionThe Standard Model of p
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Chapter 1The Standard Model of Part
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CHAPTER 1: The Standard Model of Pa
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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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