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

106 CHAPTER 5: Estimating of the Jet Energy Scale Calibration Factorm top pile-up ISR/FSR Q 2 matching Total Sys. Unc.δ sys. (∆ε estl )(%) ±0.1 ±0.1 ±0.6 ±0.4 ±0.6 ±0.9δ sys. (∆ε estb )(%) ±0.8 ±0.5 ±0.3 ±0.2 ±0.2 ±1.0Table 5.12: The systematical uncertainties on the estimated light and b jet energycorrection originating from various sources. The total uncertainty is obtained by thesquare root of the sum of the squred of the individual errors.As already noted, the estimated uncertainty on the light and b jet energy correctionsdue to the variation of the mass of the top quark are overestimated. Therefore,the uncertainties of 0.3% on the light jets and of 1.9% on the b jets are probably conservativeestimates. They are divided by a factor of 2.5 to represent the uncertaintieson the estimated jet energy corrections resulting from one sigma deviation of the topquark mass value from its world average value. Another point is that, some of theestimated systematical uncertainties quoted in Table 5.12, recieve large statistical uncertaintiesbecause they are limited with small simulated samples. For example, theestimated systematical uncertainty on the light jet energy correction due to pile-upsource, is dominated by the statistical uncertainty, since from Table 5.8 one can haveδ sys. (∆ε est∣ (%) = 0.1 ± 0.2(stat.).pile−upl )The estimated systematical uncertainty on the b jet energy correction due to eitherthe Q 2 or the matching source, is dominated by the statistical uncertainty, too.5.5 Statistical Properties of the Estimator5.5.1 Linearity of the EstimatorThe linearity of the method is checked by looking at the calibration curve, which isdefined as the variation of the estimated versus the expected jet energy corrections whileapplying an inclusive shift on the energy scales of the reconstructed jets. Applying anyrelative inclusive shift on the energy of the reconstructed jets followed by performing thekinematic fit method to constrain the event topology to fulfill the mass requirements,would yield to obtain the estimated results which are linearly dependent to the expectedjet energy corrections. This can be understood by looking at the distributions of theversus ∆E expl,bthe e+jets t¯t events.∆E estl,bwhich are shown in Figure 5.21. The plots are made using onlyIt can be seen that, when applying the L2 and L3 corrections on the input energiesof the reconstructed jets, the estimator is able to predict the expected jet energycorrections. When moving away from the point of nominal L2 and L3 corrections, adeviation of the estimated results from the expected corrections is observed resulting