[[TOC]]

= Delphes Tutorial - MC4BSM July 2016 =

== Pre-requisites ==

To successfully build Delphes the following prerequisite packages should be installed:

- gcc/tcl:

For linux users gcc/tcl should be already installed. For Mac users you should install XCode.

- ROOT:

can be downloaded from https://root.cern.ch/downloading-root
Go on latest release, and download a version under "Binary distributions".

Once it is installed, type:

{{{
source [path_to_installation]/root/bin/thisroot.sh
}}}

Then simply type in a terminal:

{{{
echo $ROOTSYS
}}}

If a path is shown then root is properly installed.

=== Part I - Getting Started ===

0) Create a tutorial directory:

{{{
mkdir DelphesTutorial
cd DelphesTutorial
}}}

1) Get Delphes:
{{{
git clone https://github.com/delphes/delphes.git
cd delphes
}}}
OR, if you don't have "git" installed, simply type (NOTE: you do not need to execute this step if you already cloned Delphes with git):
{{{
wget http://cp3.irmp.ucl.ac.be/downloads/Delphes-3.3.2.tar.gz
tar -zxf Delphes-3.3.2.tar.gz
mv Delphes-3.3.2 delphes
cd delphes
}}}
2) Install it:
{{{
./configure
make -j 4
}}}
3) Download Z' (m= 2 TeV) to WW and dijet (pT > 1 TeV) events in stdhep format
{{{
wget http://cp3.irmp.ucl.ac.be/downloads/delphes_tuto/pp_zp_ww.hep.gz
wget http://cp3.irmp.ucl.ac.be/downloads/delphes_tuto/pp_jj.hep.gz
gunzip pp_zp_ww.hep.gz
gunzip pp_jj.hep.gz
}}}

4) Finally, let's run Delphes. If the compilation went right, you should have three executables:

- DelphesLHEF  -> should not be used
- DelphesHepMC -> to be used on HepMC input format (*.hepmc)
- DelphesSTDHEP -> to be used on STDHEP input format (*.hep)

Type for instructions (note that output file comes before input file):
{{{
./DelphesSTDHEP
}}}
To run on our your input file, type:
{{{
./DelphesSTDHEP cards/delphes_card_CMS.tcl out_pp_zp_ww.root pp_zp_ww.hep
}}}
5) Open freshly produced Delphes output with ROOT, and explore it.
{{{
root -l  out_pp_zp_ww.root
TBrowser t;
}}}
In the browser, double click on the "out_pp_zp_ww.root", and then on the "Delphes" tree. Play around by double clicking on the various branches/observables.

You can then plot important observable with a simple selection with the following syntax:
{{{
Delphes->Draw("Muon.PT", "Muon.PT > 20");
Delphes->Draw("Electron.PT", "Electron.PT > 20");
}}}
- Note 1: Delphes - tree name, it can be learnt e.g. from TBrowser
- Note 2: !Muon/Electron - branch name; PT - variable (leaf) of this branch
{{{
Delphes->Draw("Jet.Mass","Electron_size + Muon_size == 1");
Delphes->Draw("Jet.Mass","Electron_size + Muon_size == 1 && Jet.PT > 500");
}}}
Objects are already ordered in PT, you can then plot the leading jet observables in this way:
{{{
Delphes->Draw("Jet[0].Mass");
Delphes->Draw("Jet[0].PT");
}}}
For more information on ROOT trees:

http://cp3.irmp.ucl.ac.be/downloads/RootTreeDescription.html

=== Part II - Understand and modify the configuration file ===

The delphes card can be schematically divided in three parts:
 - The !ExecutionPath is where the simulation/reconstruction sequence of modules is defined
 - The list of modules configurations.
 - The !TreeWriter, where the user defines which objects he stores in the output tree.

You can find an explanation for most Delphes modules here:
https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook/Modules

1. Open the card cards/delphes_card_CMS.tcl with your favorite editor and try to make sense of it.

2. Then configure the !FastJetFinder module by switching on the options for jet substructure:

{{{
###################
# Fast Jet finder
###################

module FastJetFinder FastJetFinder {
  set InputArray EFlowMerger/eflow

  set OutputArray jets

  # algorithm: 1 CDFJetClu, 2 MidPoint, 3 SIScone, 4 kt, 5 Cambridge/Aachen, 6 antikt 
  set JetAlgorithm 5 
  set ParameterR 0.8

  set ComputeNsubjettiness 1
  set Beta 1.0
  set AxisMode 4

  set ComputeTrimming 1
  set RTrim 0.2
  set PtFracTrim 0.05

  set ComputePruning 1
  set ZcutPrun 0.1
  set RcutPrun 0.5
  set RPrun 0.8

  set ComputeSoftDrop 1
  set BetaSoftDrop 0.0
  set SymmetryCutSoftDrop 0.1
  set R0SoftDrop 0.8

  set JetPTMin 20.0
}
}}}

3. Now run Delphes with the newly modified card on both the dijet and Z' samples:
{{{
./DelphesSTDHEP cards/delphes_card_CMS.tcl out_pp_zp_ww_js.root pp_zp_ww.hep
./DelphesSTDHEP cards/delphes_card_CMS.tcl out_pp_jj_js.root pp_jj.hep
}}}

4. Open the files with ROOT TBrowser as in the Getting Started section, and make sure that the new jet substructure variables are properly stored.  

5. Now [https://cp3.irmp.ucl.ac.be/projects/delphes/raw-attachment/wiki/WorkBook/Tutorials/Mc4Bsm/macro.C download] and run this simple event selection macro. It will plot two crucial jet observables that can help in discriminating between a w-jet and a light jet: the jet mass, and the N-subjettiness ratio tau2/tau1. 
{{{
root examples/macro.C'("out_pp_jj_js.root","out_pp_zp_ww_js.root")' 
}}}

6. Now improve the calorimeter resolution in the card, both energy and angular resolutions (roughly by a factor 20) 
{{{
set PhiBins {}
  for {set i -360} {$i <= 360} {incr i} {
    add PhiBins [expr {$i * $pi/360.0}]
  }

  # 0.01 unit in eta up to eta = 2.5
  for {set i -1000} {$i <= 1000} {incr i} {
    set eta [expr {$i * 0.005}]
    add EtaPhiBins $eta $PhiBins
  }


 ...

  # set ECalResolutionFormula {resolution formula as a function of eta and energy}
  # Eta shape from arXiv:1306.2016, Energy shape from arXiv:1502.02701
  set ECalResolutionFormula {                  (abs(eta) <= 1.5) *0.05*(1+0.64*eta^2) * sqrt(energy^2*0.008^2 + energy*0.11^2 + 0.40^2) +
                             (abs(eta) > 1.5 && abs(eta) <= 2.5) *0.05* (2.16 + 5.6*(abs(eta)-2)^2) * sqrt(energy^2*0.008^2 + energy*0.11^2 + 0.40^2) +
                             (abs(eta) > 2.5 && abs(eta) <= 5.0) *0.05* sqrt(energy^2*0.107^2 + energy*2.08^2)}


}}}

7. Re-run Delphes simulation and macro.C with the new configuration and appreciate the effect of improved resolution on the final distributions:
{{{
./DelphesSTDHEP cards/delphes_card_CMS.tcl out_pp_zp_ww_js_nc.root pp_zp_ww.hep
./DelphesSTDHEP cards/delphes_card_CMS.tcl out_pp_jj_js_nc.root pp_jj.hep
root examples/macro.C'("out_pp_jj_js_bc.root","out_pp_zp_ww_js_bc.root")' 
}}}