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

112 CHAPTER 5: Estimating of the Jet Energy Scale Calibration Factor– Subsequently the candidate electron is required to have an absolute impactparameter d 0 less than 0.02 cm.– Also the electron is asked to fulfill the identification criteria which weredescribed in Section 4.4.1. The cut values are the same as before so that anidentification efficiency of about 70% can be obtained.– The final criteria that the candidate electron should fulfill is applied on therelIso variable. The definition of the relIso variable was already given inSection 4.4.1. The electron is asked to have a relIso value less than 0.1.• The event is rejected if it contains any isolated muon, which is defined as a globalmuon with a p T exceeding 10 GeV and located within |η| < 2.5. The isolationcriteria is applied on the relative isolation variable and the candidate muon isdefined as isolated if its relIso variable is less than 0.2. In case such muon existswithin the event, that event is rejected.• In this step, the events which happen to be in the peak of the mass distributionof the Z boson are removed. The invariant mass of the selected isolated electronand an other loose electron is calculated. If the resulting invariant mass is withinthe range of 76 GeV to 106 GeV, the event is rejected. The loose electron isdefined using the same variables as given in Section 4.4.1.• There is another additional requirement which is applied on the selected electron.Electrons can be initiated from various sources in the event. For example, itis possible that the electron originates from a converted photon. Photons canproduce an electron-positron pair while traversing the tracker material. Thereforethere is a probability that the selected electron initiates from a photon conversion.In order to reject the electrons which come out of a conversion process, somealgorithms are developped within the CMS collaboration. The algorithm startsby looking for a partner track reconstructed very close to the selected electron.Since the electron and positron initiated from a converted photon bend in oppositedirection due to the presence of the magnetic field, it is required that the partnertrack has an opposite charge with respect to the electron track. If the distancebetween the two tracks is less than a pre-defined value, the selected electron isflagged as conversion. The detailed information of the technical implementationcan be found in [105].• The event is required to have at least 4 reconstructed calorimeter jets. The jetsare reconstructed using the anti-k T algorithm where the cone radius is set to be0.5 as before. It should be noted that the jets are L2 and L3 corrected. Theselected jets should fulfill the following requirements.– A tighter cut on the transverse momentum of the reconstructed jets is appliedcompared to the cut which has been applied in the pre-selection step.The jets are asked to have p T > 30 GeV . The threshold cut on the pseudorapidityvariable of the jets is the same as the one applied in the pre-selectionstep, |η| < 2.4.