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

CHAPTER 3: Object Reconstruction 39Figure 3.7: Comparison between the L3 calibration curve derived from the simulationand the Z+jet balance method applied on collision data, and the ratio of the twocorrections [73].L2 Relative η Correction• Method with SimulationThe purpose of the L2 correction is to correct jets at arbitrary η relative to acontrol region where the absolute calibration is easier. As a consequence of theL2 correction, the jet response becomes flat as a function of the pseudorapidity.In order to derive the L2 correction factors from the simulation, it is essential tocalculate the η dependent L3 absolute correction, C abs. (η, p CaloJetT ), as introducedabove. This is achieved by repeating exactly the same procedure described in the“L3 Absolute p T Correction” part for multiple η regions.The relative correction is defined asC rel. (η, p CaloJetT) = pcontrol T,p CaloJetTwhere p controlT and p CaloJetT are the measured transverse momenta of a GenJet ofthe same p GenJetT in the control region and in an arbitrary η region, respectively.Starting from a reconstructed CaloJet with arbitrary η and with p CaloJetT , theabsolute correction obtained for that specific η region can be used to find thetrue value of the CaloJet p T , being p GenJetTp GenJetT= p CaloJetT× C abs. (η, p CaloJetT ).Then with the use of the response of the detector in the control region, one canfind the value of the reconstructed CaloJet p T in the control region for the samep GenJetTp controlT= R(control, p GenJetT ) × p GenJetT .