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

More documents

Recommendations

Info

58 CHAPTER 4: Reconstructing and Selecting Physics Event#Events510410tt+jets semi-ele (2717.3 entries)tt+jets other (7215.5 entries)t+jets, (all channels) (712.5 entries)Z+jets (8215.9 entries)W+jets (14446.5 entries)Multi-jets (7191770.9 entries)#Events510410tt+jets semi-ele (1866.6 entries)tt+jets other (5423.5 entries)t+jets, (all channels) (554.9 entries)Z+jets (4721.2 entries)W+jets (12499.7 entries)Multi-jets (6668437.6 entries)310310210210101011-1100 1 2 3 4 5Electron RelIsoFigure 4.8: Relative isolation variable ofall reconstructed electrons for the eventspassed primary vertex cut.-1100 1 2 3 4 5Leading Electron RelIsoFigure 4.9: Relative isolation variable ofthe electron with the maximum p T for theevents passed primary vertex cut.– ∆η in which is defined as the η difference between the supercluster and thecorresponding track extrapolated to the ECAL starting from the interactionvertex. Depending on the position of the reconstructed electron, a barrelelectron is asked to have a ∆η in less than 0.004 while for the endcap electronthis value is set to be 0.005.– ∆φ in which is defined as the φ difference between the supercluster and thecorresponding track extrapolated to the ECAL starting from the interactionvertex. Depending on the position of the reconstructed electron, a barrelelectron is asked to have a ∆φ in less than 0.03 while for the endcap electronthis value is set to be 0.02.– σ iηiη is a measure of the shower width in a direction which is very largelyunaffected by showering of electrons in the tracker material and so has beena key variable in electron identification. Depending on the position of thereconstructed electron, a barrel electron is asked to have a σ iηiη less than0.01 while for the endcap electron this value is set to be 0.03.• Finally, the selected electron is required to have d 0 < 0.02 cm where d 0 is definedas the distance of the reconstructed track of the electron in the transverse plainwith respect to the beam spot. This variable is useful in differentiating betweenprompt electrons and those which are produced in jets. The electrons appearingin jets usually have larger d 0 values. Hence cutting on this variable would rejectmost of the QCD events.A summary of the cut values applied on the various identification variables of theselected electron is given in Table 4.4.
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.
Page 1:
Vrije Universiteit BrusselFaculteit
Page 5 and 6:
IntroductionThe Standard Model of p
Page 7 and 8:
Chapter 1The Standard Model of Part
Page 9 and 10:
CHAPTER 1: The Standard Model of Pa
Page 11 and 12: CHAPTER 1: The Standard Model of Pa
Page 19 and 20: Chapter 2The CMS experiment at the
Page 21 and 22: CHAPTER 2: The CMS experiment at th
Page 33 and 34: Chapter 3Object ReconstructionThe e
Page 35 and 36: CHAPTER 3: Object Reconstruction 31
Page 51 and 52: Chapter 4Reconstructing and Selecti
Page 53 and 54: CHAPTER 4: Reconstructing and Selec
Page 61: CHAPTER 4: Reconstructing and Selec
Page 71 and 72: Chapter 5Estimating of the Jet Ener
Page 73 and 74: CHAPTER 5: Estimating of the Jet En
Page 91 and 92: 2χ / ndf18.76 / 7p0 9.492e-08 ±9.
Page 113 and 114:
CHAPTER 5: Estimating of the Jet En
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Chapter 6ConclusionThe Standard Mod
Page 133 and 134:
CHAPTER 6: Conclusion 129The method
Page 135 and 136:
Bibliography[1] M. E. Peskin and D.
Page 137 and 138:
BIBLIOGRAPHY 133[40] The ALICE Coll
Page 139 and 140:
BIBLIOGRAPHY 135[76] The CMS Collab
Page 141 and 142:
SummaryJets appear in the final sta
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?