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

CHAPTER 4: Reconstructing and Selecting Physics Event 59h/e ∆η in ∆φ in σ iηiηbarrel endcap barrel endcap barrel endcap barrel endcapcut value 0.025 0.025 0.004 0.005 0.03 0.02 0.01 0.03Table 4.4: Required cut values on the identification variables of the selected electron.The distributions of the shower shape variables together with the d 0 parameter ofall reconstructed electrons in those events that already passed the primary vertex cut,can be found in Figure 4.10.As it is seen from Figure 4.10, the distribution of the ∆η in variable is sharper comparedto the ∆φ in distribution, representing the radiated electrons which bend in theφ-direction due to the magnetic field in the z-direction.Also the multiplicity of the selected electrons per event which already passed the primaryvertex cut, is shown in Figure 4.11.It can be seen from Figure 4.11 that most of the QCD multijet events do notcontain a selected electron while two selected electrons can be found in Z+jets eventsor t¯t → other, as expected.Those events with Nesel = 1, corresponding to the situation that exactly one selectedelectron is present per event, are accepted for further analysis.Second Electron VetoSome of the backgrounds such as Z+jets events where Z → e + e − or backgroundscoming from full leptonic decay of t¯t events of which both of leptons are electrons,contain more than one electron in their final states. Hence vetoing of the presence of asecond electron can suppress these kind of backgrounds. For the second electron, thereare some looser cuts applied so that the background rejection efficiency is increased.The p T cut is lowered to 20 GeV compared to the selected electron. The cut thresholdson the different identification parameters are also loosen and are listed in Table 4.5.No isolation requirement neither d 0 cut is applied on the second electron.The multiplicity of the second loose electron per event, excluding the selected electron,is shown in Figure 4.12.The event is rejected if it has at least one second loose electron as defined above.