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

CHAPTER 5: Estimating of the Jet Energy Scale Calibration Factor 99∆ε expl/b. The estimation of the residual jet energy corrections would be well done ifthe bias would be equal to zero. The estimated as well as the expected results of theresidual jet energy corrections are collected and the corresponding bias for the lightand the b jets is calculated which can be found in Table 5.6.∆ε expl(%) ∆ε estl(%) ∆ε estl− ∆ε expl(%)-8.67±0.23 -10.12±0.13 -1.45±0.26∆ε expb(%) ∆ε estb(%)∆ε estb− ∆ε expb(%)-2.08±0.36 -1.31±0.20 0.77±0.41Table 5.6: The final estimated residual jet energy corrections obtained for 100pb −1 .The corresponding expected residual corrections and the possible bias are also shown.Taking into account the systematical uncertainties on the expected light and b jetcorrections, mentioned in Table 5.5, would result to obtain a bias on, for example, theestimated b jets to be compatible with zero. Other systematical uncertainties on theestimated residual light and b jet energy corrections are calculated in Section 5.4.2.5.4.1 Performance of the MethodAs discussed in Section 5.1.6, the distributions of the reconstructed W boson and topquark masses in the topology of the e+jets t¯t events are shifted from the values that wereused in the simulation which consequently motivates the need for residual jet energycorrections. Since in the hadronic branch of the e+jets t¯t event, t → Wb → q¯qb, bothlight jets, arising in the decay of the hadronic W boson, and b jets, originating from thedecay of the hadronic top quark, are present. Then by imposing the mass constraintsof both the W boson and the top quark by means of a kinematic fit approach, onecould estimate the residual light as well as the b jet energy corrections as described inSection 5.2. The aim of the method was to correct the energies of the reconstructedjets in the hadronic branch of the e+jets t¯t topology so that the resulting reconstructedW boson and top quark masses are peaked around the nominal parameters which havebeen used to generate the event.The plots shown in Figure 5.20 are the invariant masses of the corrected four-vector ofthe W boson and top quark which are reconstructed from the corrected four-vectors ofthe reconstructed jets in the final state of e+jets t¯t events. The events for which a truejet-parton combination found by the MVA method, are used to fill the distributions.Compared to the plots obtained in Figure 5.9, it is obvious that the corrected massdistributions are peaked around their nominal values as it was aimed. The reconstructedmass values of the W boson and the top quark can be further improved byapplying a second iteration which is explained in the following. The estimated residual