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

CHAPTER 3: Object Reconstruction 41be applied on the CaloJet p T reconstructed outside the barrel. This makes thecalorimeter response to jets flat as a function of η and equal to the value obtainedfor the jets which are reconstructed in the control region.The resulting relative response function obtained from dijet balancing is comparedwith the one derived from the simulation study, which is shown in Figure3.9. The agreement between these two confirms the validity of the proposeddata driven method.Figure 3.9: The relative jet response as a function of η from both the dijet balancemethod and the simulation for 200 GeV < p dijetT< 300 GeV [73].3.2.4 Jet Energy ResolutionNow that jets are corrected, it is the time to check how successful the correction stepsL2 and L3 are. Jet energy resolution is the uncertainty on the measured jet energy afterapplying the required corrections. Different methods for extracting the resolutions onthe energy of the jets exist and are discussed below [76].• Method with SimulationSo-called Monte Carlo resolutions are obtained from simulated data by plottingthe distributions of the ratio between the corrected CaloJet p T and the correspondingGenJet p T as a function of the p T of the GenJet. The CaloJets arespatially matched to the GenJets with ∆R = √ (∆η) 2 + (∆φ) 2 < 0.25. Eachdistribution is subsequently fitted with a Gaussian and the width of the fit isused as the resolution for that particular p T bin.Figure 3.10 shows a generic distribution of the jet response after applying L2 andL3 corrections, overimposed with a fitted Gaussian function.• Data Driven MethodThe data driven method for calculating the jet p T resolutions is based on QCD