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

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102 CHAPTER 5: Estimating of the Jet Energy Scale Calibration Factorestimated jet energy corrections for the events with and without including pile-up aregiven.∆ε expl(%) ∆ε estl (%) ∆ε estl − ∆ε expl(%)nominal -9.38±0.25 -8.75±0.14 0.63±0.29pile-up -9.52±0.24 -8.68±0.13 0.84±0.27∆ε expb(%) ∆ε estb (%)∆ε estb− ∆ε expb(%)nominal -2.66±0.36 -2.81±0.20 -0.15±0.41pile-up -2.82±0.36 -3.30±0.20 -0.48±0.41Table 5.8: The expected and estimated residual jet energy corrections and the bias onthe estimations in the presence of pile-up events. The nominal refers to the situationwhen no pile-up is present.As it is seen from Table 5.8, the method of estimating the residual jet energy correctionsis stable with respect to adding the pile-up collisions. Obviously the expected aswell as the estimated corrections are affected by the pile-up collisions. If the pile-up iswell simulated, the bias should be stable. The estimated residual light and b jet energycorrections do not change much in the presence of the pile-up events. The estimatedlight jet energy correction changes from -8.75%, corresponding to the nominal value,to -8.68%, which is obtained when including pile-up events. Thus, the shift of 0.07%is considered as the systematic uncertainty on the estimated residual light jet energycorrection due to the pile-up effects. The deviation of the estimated b jet energy correctionfrom the nominal value corresponds to 0.49% which is taken as the systematicuncertainty on the estimated residual b jet energy correction due to the pile-up events.ISR/FSRWhen simulating physics events, various parameters are set to control the productionand decay products of the hard scattering interactions. Changing any of these parametersindividually, would yield to obtain a different topology of the event. Therefore,the sensitivity of the estimated results with respect to the changes of these parameters,has to be studied and the possible deviations are taken as the systematic uncertaintieson the final estimation. For example, the amount of ISR/FSR that are allowed to begenerated in the simulation procedure can affect the results. Two different sampleswith a smaller and larger amount of radiation compared to the nominal situation areprocessed. The estimated residual jet energy corrections are obtained for each of thesesamples which are given in Table 5.9. The estimated and expected results for light andb jet energy corrections are listed individually for the various samples.
CHAPTER 5: Estimating of the Jet Energy Scale Calibration Factor 103∆ε expl(%) ∆ε estl(%) ∆ε estl− ∆ε expl(%)nominal -9.38±0.25 -8.75±0.14 0.63±0.29larger ISR/FSR -8.85±0.26 -8.12±0.14 0.73±0.29smaller ISR/FSR -9.62±0.25 -9.13±0.14 0.49±0.29∆ε expb(%) ∆ε estb(%)∆ε estb− ∆ε expb(%)nominal -2.66±0.36 -2.81±0.20 -0.15±0.41larger ISR/FSR -2.54±0.37 -2.68±0.20 -0.14±0.42smaller ISR/FSR -1.85±0.39 -2.49±0.20 0.64±0.44Table 5.9: The expected and estimated residual jet energy corrections and the bias onthe estimations for the samples with larger and smaller amount of radiation comparedto the nominal.Since the bias on the estimated light and b jet energy corrections is small and,in some cases, is compatible with zero within the statistical uncertainties, it can bededuced that the method is stable with respect to changes in ISR/FSR. The estimatedlight jet energy correction changes from -8.12%, corresponding to the sample withlarger ISR/FSR, to -9.13%, which is obtained when considering smaller amount ofISR/FSR in the simulation procedure. Compared to the nominal value which equals-8.75%, the maximum deviation of the estimated light jet energy correction is takenas the systematic uncertainty due to the ISR/FSR, being 0.63%. In case of b jets, themaximum deviation would reach to 0.32% which is quoted as the systematic uncertaintyon the estimated b jet energy correction due to the ISR/FSR.Scale Factor Q 2As already mentioned, the initial and final state radiations are governed by the use ofthe DGLAP equation which describes the evolution of the partonic distribution functionas a function of the factorization scale Q 2 . According to the DGLAP equation, the finalstate radiation in an event can be started from a maximum energy state Q 2 max, whichis chosen to be the squared mass of the parton shower initiator, down to smaller valuesof the Q 2 scale. Since the chosen value used for the Q 2 max parameter might not be theoptimal choice for the description of observed proton-proton collision data, the effects ofaltering the Q 2 value up and downwards are taken into account. Therefore, additionalsamples are simulated for which the initial input variable of the Q 2 max parameter ischanged within an interval. Then, in order to check the effects of the variation ofthe Q 2 scale, the method of estimating the residual jet energy corrections is appliedon both simulated samples with the various settings of the Q 2 parameters and thenominal sample which is simulated with the pre-defined setting of the Q 2 parameter.The results of the estimated and expected residual jet energy corrections on differentsettings of the Q 2 scale are summarized and a possible bias of the method is calculated
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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 2The CMS experiment at the
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CHAPTER 2: The CMS experiment at th
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Chapter 3Object ReconstructionThe e
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Chapter 4Reconstructing and Selecti
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