= The first !MadAnalysis 5 workshop on LHC recasting @ Korea =
= Analysis 8: ATL-PHYS-PROC-2O16-117 =

||= Students =|| Flacke Thomas, Jeong Yong Ho, Kim Minho, Kim U-Rae || 
||= 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
  * 3.2. 2 pairs of opposite sign 
  * 3.3. At least one pair must have same flavour leptons
  * 3.4. We define Z1 = reconstructed Z from opposite-sign same-flavour pair the closest to the Z mass. We define Z2 = reconstructed Z from the other pair (same-flavour or not).
  * 3.5. Defining 4 signal regions according the final states:
    * 4l-DF-1b
    * 4l-DF-2b
    * 4l-SF-1b
    * 4l-SF-2b
  * 3.5. Cut on PT34 = scalar sum of the transverse momenta of the leptons used in Z2:
    * [4l-DF-1b]: PT34 > 35 GeV
    * [4l-SF-1b]: PT34 > 25 GeV
  * 3.6. MET:
    * [4l-SF-1b]: If |MZ2-MZ| > 10 GeV then imposing MET > 40 GeV else imposing MET > 80 GeV
    * [4l-SF-2b]: If |MZ2-MZ| < 10 GeV then imposing MET > 40 GeV
  * 3.7. Number of b-jets:
    * [4l-DF-1b]+[4l-SF-1b]: #b-jets = 1
    * [4l-DF-2b]+[4l-SF-2b]: #b-jets >= 2

=== 3.4 Definition of exotic observables ===

No exotic observables.

== 3. Detector simulation ==

Official Delphes package could be enough.

To improve the realism of the simulation, Delphes_Track could be used for cutting on D0. Is it necessary? To try...

== 4. Validation material ==

=== 4.1 Monte-Carlo samples ===

* LO (but xsections are normalized to NLO)
* Model used: SM
  * Mtop = 172.5 GeV
  * Mhiggs = 125 GeV
  * processes = ttZ (including gamma*) & ttW (but no ttWW)
  * xsections: Table 5 of ATL-PHYS-PUB-2016-005
* MC generator program (name + version): MG5_aMC
* Shower program (name + version): Pythia v8.210
* Tune of Pythia: A14 tune (see http://cds.cern.ch/record/1966419)
* PDF set: NNPDF2.3LO
* ME/PS merging????

=== 4.2 Reference plots / cut-flows ===

* MC xsections and plots: http://cds.cern.ch/record/2120826/files/ATL-PHYS-PUB-2016-005.pdf?version=1:
  * Table 5
  * Figure 5

* Final number of signal events after the selection in each signal region:
  * https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2015-22/tabaux_06.pdf

* Plots for Analysis 1: SS-muons:
  * Figure 1 of the paper

* Plots for Analysis 2: trileptons
  * Figure 5 of the paper

* Plots for Analysis 3: tetraleptons
  * Figure 6 of the paper

* Rivet analyses


== 4. Validation results ==

== 5. Reinterpretation (optional) ==

== 6. Questions / issues ==