The first MadAnalysis 5 workshop on LHC recasting @ Korea

Analysis 8: ATL-PHYS-PROC-2O16-117

Students
Supervisor(s)	Eric Conte	Benjamin Fuks

1. Analysis summary

A measurement of the tt¯Z and tt¯W production cross sections in final states with:

• two same-charge muons: one muon coming from Z/W and one from the top decay.
• or three leptons (electrons or muons),
• or four leptons (electrons or muons): only ttZ case where Z and the 2 top quarks are decaying leptonically.

The analysis uses a data sample of proton-proton collisions at s√=13 TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015, corresponding to a total integrated luminosity of 3.2 fb−1. The inclusive cross sections are extracted using likelihood fits to signal and control regions, resulting in σtt¯Z=0.9±0.3 pb and σtt¯W=1.5±0.8 pb, in agreement with the Standard Model predictions.

2. Analysis global information

• ATLAS contact person: nobody
• Center of mass energy: 13 TeV
• Integrated luminosity: 3.2 fb−1
• Link to arXiv: ​https://arxiv.org/abs/1609.01599
• Link to the collaboration page: ​https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2015-22/
• Link to CDS: ​https://cds.cern.ch/record/2211022?ln=fr
• Link to Inspire: ​http://inspirehep.net/record/1485353
• Link to Rivet analyses: ​https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2016-005/

3. Selection description

3.1 Trigger selection

Only events using single-electron OR single-muon triggers are accepted:

• single-electron: one electron with pT > 24 GeV
• single-muon: one muon with pT > 20 GeV

PS: This part cannot usually be described by the fast-simulation of detector.

3.2 Object definition

• electron:
  • pT > 7 GeV,
  • |eta|<2.47. Are excluded electrons in the end-cap, i.e. 1.37 < |eta| < 1.52.
  • 'medium' likelihood identification.
  • transverse impact parameter: |d0|/err(d0) < 5.
  • longitudinal impact parameter: |z_0 x sin\theta | < 0.5 mm
  • isolation criterion:
    • sum PT of tracks in a cone around the electron (the electron track is subtracted) of size = min(10 GeV/PT,0.2) < 6% electron PT.
    • sum ET of clusters in a cone around the electron (the electron cluster is subtracted) of size DR=0.2 < 6% electron PT.

• muon:
  • pT > 7 GeV
  • |eta|<2.4
  • 'medium' identification.
  • transverse impact parameter: |d0|/err(d0) < 3.
  • longitudinal impact parameter: |z_0 x sin\theta | < 0.5 mm
  • isolation criterion: sum PT of tracks in a cone around the muon (the muon track is subtracted) of size = min(10 GeV/PT,0.3) < 6% muon PT.

• jet:
  • clustering: anti-kT with =0.4
  • pT > 25 GeV
  • |eta|<2.5
  • Pile-up rejection: jets with pT < 60 GeV and |η| < 2.4 are required to satisfy pile-up rejection criteria (JVT)

• b-jet: MV2c20 algorithm. In simulation, the tagging algorithm gives a rejection factor of about 130 against light-quark and gluon jets, and about 4.5 against jets containing charm quarks.

• preventing double-counting:
  • the closest jet within DR=0.2 cone of an electron is removed.
  • if, after the previous selection cut, the nearest jet of an electron is in DR=0.4 cone, then the electron is removed.
  • muons in a DR=0.4 cone around a given jet are removed. BUT if the jet has fewer than three associated tracks, the muon is kept.

3.3 Cut-flow chart

• Common:

• 0. Trigger confirmation: at least one lepton (muon/electron) with PT > 25 GeV

• 1. Analysis 1: SS-muons

• 1.1. 2 muons of same charge, with PT > 25 GeV
• 1.2. Events with additional leptons are vetoed
• 1.3. MET > 40 GeV
• 1.4. HT > 240 GeV
• 1.5. At least 2 b-jets

• 2. Analysis 2: trilepton analysis

• 2.1. Exactly 3 leptons
• 2.2. 2 opposite sign, same flavour leptons, and
• 2.2. Leading lepton with PT > 25 GeV, the other leptons with PT > 20 GeV
• 2.3. Defining 4 signal regions according the final states:
  • 3l-Z-1b4j
  • 3l-Z-2b3j
  • 3l-Z-2b4j
  • 3l-noZ-2b
• 2.4. Compatibility with a Z:
  • [3l-Z-1b4j]+[3l-Z-2b3j]+[3l-Z-2b4j]: compatible with a Z i.e. (invM-MZ)<10 GeV
  • [3l-noZ-2b]: not compatible with a Z i.e. (invM-MZ)>10 GeV
• 2.5. Number of light jets (no b-jet):
  • [3l-Z-2b3j]: #jets = 3
  • [3l-Z-1b4j]+[3l-Z-3b4j]: #jets >= 4
  • [3l-noZ-2b]: #jets = 2, 3 or 4
• 2.6. Number of b-jets:
  • [3l-Z-1b4j]: #b-jets = 1
  • [3l-Z-2b3j]+[3l-Z-3b4j]+[3l-noZ-2b]: #b-jets >= 2

• 3. Analysis 3: tetralepton analysis

• 3.1 Exactly 4 leptons

3.4 Definition of exotic observables

Like SUSY transverse observable. Notice that classical MT2 & MT2W are encoded within the MadAnalysis framework.

3. Detector simulation

Can we use the last release of the Delphes package with the CMS/ATLAS MA5tune-card? or do need to improve the simulation?

4. Validation material

4.1 Monte-Carlo samples

• LO/NLO?
• Model used:
• MC generator program (name + version):
• Shower program (name + version):
• Tune of Pythia:
• PDF set:
• ME/PS merging????

4.2 Reference plots / cut-flows

• List of validation material

4. Validation results

5. Reinterpretation (optional)

6. Questions / issues