Simulation of the Measurement of the Inclusive Jet Cross Sections in Z(ee/mumu)+jets Events in pp Collisions at 14TeV with the ATLAS experiment.

E.Segura thesis (June 2009)

Here is the final version of my PhD thesis, in ps format (here) and pdf fomat (here).

Z+ jets Plots for the CSC note (2008):

Here are the plots from Z+jets Analysis, including Z->ee and Z->μμ (CSC note: "Measurement of Z+jets Cross-Section at ATLAS") for future conferences (plots "blessed" at Atlas SM meeting on 2nd July 2008 (link))

Data Samples used: Zee + jets

Process	Generator	Dataset
signal Z -> ee	Alpgen/Herwig	8130 - 8135
QCD dijets JF17	Pythia	5802
Top	Pythia	5568
W -> e ν	Pythia	5104
Z-> ττ	Pythia	5146

Data Samples used: Zμμ +jets

Process	Generator	Dataset
signal Z -> μμ	Alpgen/Herwig	8142-8147
QCD dijets (bb(μμ))	Pythia	17506
Top	Pythia	5568
W -> μ ν	Pythia	5105
Z-> ττ	Pythia	5904

Event Selection: Zee +jets

• Two electrons with PT > 25 GeV in |η| < 2.4, excluding 1.37 < |η| <1.52 (barrel-to-endcap calorimeter crack region)
• medium electron-ID signature
• deltaR (electron, electron) > 0.2
• Jet cuts (using Calorimeter Tower Cone 0.4 jet algorithm):
  • PT > 40 GeV
  • |η| < 3.0
  • Remove jets which are within ΔR = 0.4 of the electron
  • Invariant mass cut: 81-101GeV

Event Selection: Zμμ +jets

• Two muons with PT > 15 GeV in |η| < 2.4 & |η| > 0.1 (holes for service passages) & outside 1.2 < |η| <1.3 (some MDT-chambers missing in the initial-layout of the Muons Spectrometer)
• Isolation: Energy in the ΔR = 0.2 cone around muon < 15 GeV
• Jet cuts (using Topological Cluster Cone 0.4 jet algorithm):
  • PT > 40 GeV
  • |η| < 3.0
  • Remove jets which are within ΔR = 0.4 of the muon
  • Invariant mass cut: 81-101GeV

Lepton reconstruction in the presence of jets

• deltaR (electron, jet) (.eps)(.png):
  

• deltaR (electron, electron) (.eps) (.png):
  

Signal and Background: Zee +jets

Distributions of the di-electron mass, inclusive jet multiplicity, PT of the leading and second leading jet in the electron channel for L = 1fb-1.

• Z(e,e) invariant mass for signal + background (.eps) (.png):
  

• Inclusive jet multiplicity (signal+background) (.eps) (.png):
  

• PT leading jet distribution for signal+backgrounds (.eps) (.png):
  

• PT 2nd leading jet for signal+backgrounds (.eps) (.png):
  

Signal and Background: Zμμ +jets

Distributions of the di-muon mass, inclusive jet multiplicity, PT of the leading jet and second leading jet for signal and backgrounds in the muon channel. In order to provide higher statistics for the background determination, background events in an invariant mass of 51 - 131 GeV, are scaled down for an invariant mass window of 81 - 101 GeV.

• Z(mu,mu) invariant mass for signal + background (.eps) (.png):
  

• Inclusive jet multiplicity (signal+background) (.eps) (.png):
  

• PT leading jet distribution for signal+backgrounds (.eps) (.png):
  

• PT 2nd leading jet distribution for signal+backgrounds (.eps) (.png):
  

Correction from parton to hadron level

MCFM predictions have to be corrected with respect to non-perturbative effects of fragmentation and underlying event (UE), from parton level to hadron level. Cone 0.4 jet algorithm has been used.

• Fragmentation correction (.eps)(.png):
  

• Fragmentation + Underlying Event correction (.eps)(.png):
  

Unfolding detector effects

Comparison of the distribution of the PT of the leading jet and the 2nd leading jet for the generated Monte Carlo and for the reconstructed quantities without any correction, after the corrections for electron triggering and reconstruction and after applying in addition the jet-related corrections.

• Leading jet (.eps)(.png):
  

• Second leading jet (.eps)(.png):
  

Comparison of MCFM predictions and Alpgen/Pythia (at hadron level)

Comparison of the inclusive jet cross-section and the PT of the leading jet and of the 2nd leading jet for the Zμμ +jets channel for PYTHIA and ALPGEN Monte Carlo with NLO (LO) MCFM predictions.

• Inclusive jet cross-section (.eps)(.png):
  

• PT leading jet (.eps)(.png):
  

• PT 2nd leading jet (.eps)(.png):
  

JES uncertainty

• JES uncertainty on Jet Multiplicity for Zμμ (.eps)(.png) and (.eps)(.png)
  

• JES uncertainty on Leading Jet PT for Zμμ (.eps)(.png) and (.eps)(.png):
  

Analysis simulation results

Comparion for the Zee +jets channel of the inclusive jet multiplicity and the PT of the leading jet for MCFM and the fully-simulated corrected ALPGEN data. The errors on the MCFM predictions result from the PDF uncertainty and from the errors of the non-perturbative effect corrections. The errors on the ALPGEN sample include all the statistical and systematic uncertainties (JES 5%).

• Inclusive Jet Multiplicity (.eps)(.png):
  

• PT leading jet (.eps)(.png):
  

Statistical and Systematic Limitations

Uncertainty on the ratio of the measurement and the theory for the inclusive jet cross-section and the PT of the leading jet for Zee +jets process.

• Uncertainty on the inclusive jet cross-section (.eps)(.png):
  

• Uncertainty on the PT of the leading jet (.eps)(.png):
  

- EsterSegura - 29 Jul 2008