Quick start with Delphes
========================


Commands to get the code:

   wget --no-check-certificate https://cp3.irmp.ucl.ac.be/projects/delphes/raw-attachment/wiki/WikiStart/Delphes-3.0.0.tar.gz

   tar -zxf Delphes-3.0.0.tar.gz

Commands to compile the code:

   cd Delphes-3.0.0

   make -j 4

Finally, we can run Delphes:

   ./DelphesHepMC
   
and simulate some Z->ee events:

   ./DelphesSTDHEP examples/delphes_card_CMS.tcl delphes_output.root examples/z_ee.hep

or

   curl -s http://cp3.irmp.ucl.ac.be/~demin/z_ee.hep.gz | gunzip | ./DelphesSTDHEP examples/delphes_card_CMS.tcl delphes_output.root


Simple analysis using TTree::Draw
=================================


Now we can start ROOT and look at the data stored on the tree

Start ROOT and load shared library:

   root -l
   gSystem->Load("libDelphes");

Open ROOT tree file and do some basic analysis using Draw or TBrowser:

   TFile::Open("delphes_output.root");
   Delphes->Draw("Electron.PT");
   TBrowser browser;

Note 1: Delphes - tree name, it can be learnt e.g. from TBrowser

Note 2: Electron - branch name; PT - variable (leaf) of this branch

Complete description of all branches can be found in

   Delphes/doc/RootTreeDescription.html

This file is also available via web:

   http://cp3.irmp.ucl.ac.be/~demin/RootTreeDescription.html


Macro-based analysis
====================


Analysis macro consists of histogram booking, event loop (histogram filling),
histogram display

Let's simulate some bbbar events:

   ./DelphesSTDHEP examples/delphes_card_CMS.tcl delphes_output.root examples/bbar.hep

or

   curl -s http://cp3.irmp.ucl.ac.be/~demin/bbar.hep.gz | gunzip | ./DelphesSTDHEP examples/delphes_card_CMS.tcl delphes_output.root

Start ROOT and load shared library:

   root -l
   gSystem->Load("libDelphes");

Basic analysis macro:

{
  // Create chain of root trees
  TChain chain("Delphes");
  chain.Add("delphes_output.root");
  
  // Create object of class ExRootTreeReader
  ExRootTreeReader *treeReader = new ExRootTreeReader(&chain);
  Long64_t numberOfEntries = treeReader->GetEntries();
  
  // Get pointers to branches used in this analysis
  TClonesArray *branchJet = treeReader->UseBranch("Jet");

  // Book histograms
  TH1 *histJetPT = new TH1F("jet_pt", "jet P_{T}", 100, 0.0, 100.0);

  // Loop over all events
  for(Int_t entry = 0; entry < numberOfEntries; ++entry)
  {

    // Load selected branches with data from specified event
    treeReader->ReadEntry(entry);
  
    // If event contains at least 1 jet
    if(branchJet->GetEntries() > 0)
    {
      // Take first jet
      Jet *jet = (Jet*) branchJet->At(0);
      
      // Plot jet transverse momentum
      histJetPT->Fill(jet->PT);
      
      // Print jet transverse momentum
      cout << jet->PT << endl;
    }

  }

  // Show resulting histograms
  histJetPT->Draw();
}


More advanced macro-based analysis
==================================


Delphes/examples contains macros Example1.C and Example2.C

Here are commands to run these macros:

   root -l
   gSystem->Load("libDelphes");
   .X examples/Example2.C("delphes_output.root");


Modifying configuration file
============================


Open default configuration file in an editor:

   vi examples/delphes_card_CMS.tcl

Replace the default b-tagging efficiency formulas with the the new ones:

  # default efficiency formula (misidentification rate)
  add EfficiencyFormula {0} {0.001}

  # efficiency formula for c-jets (misidentification rate)
  add EfficiencyFormula {4} {                                      (pt <= 15.0) * (0.000) + \
                                                (abs(eta) <= 1.2) * (pt > 15.0) * (0.2*tanh(pt*0.03 - 0.4)) + \
                              (abs(eta) > 1.2 && abs(eta) <= 2.5) * (pt > 15.0) * (0.1*tanh(pt*0.03 - 0.4)) + \
                              (abs(eta) > 2.5)                                  * (0.000)}  
  
  # efficiency formula for b-jets
  add EfficiencyFormula {5} {                                      (pt <= 15.0) * (0.000) + \
                                                (abs(eta) <= 1.2) * (pt > 15.0) * (0.5*tanh(pt*0.03 - 0.4)) + \
                              (abs(eta) > 1.2 && abs(eta) <= 2.5) * (pt > 15.0) * (0.4*tanh(pt*0.03 - 0.4)) + \
                              (abs(eta) > 2.5)                                  * (0.000)}

Now we can run Delphes with the modified configuration file:

   ./DelphesSTDHEP examples/delphes_card_CMS.tcl delphes_output_new.root examples/bbar.hep

or

    curl -s http://cp3.irmp.ucl.ac.be/~demin/bbar.hep.gz | gunzip | ./DelphesSTDHEP examples/delphes_card_CMS.tcl delphes_output_new.root

Open ROOT tree file and check the PT spectrum of the b-jets:

   root -l
   TFile *file = TFile::Open("delphes_output.root");
   Delphes->Draw("Jet.PT", "Jet.BTag == 1");
   
   file->Close();
   
   TFile *file = TFile::Open("delphes_output_new.root");
   Delphes->Draw("Jet.PT", "Jet.BTag == 1", "SAME");

   htemp->SetLineColor(2);
   htemp->Draw("SAME");
   
   file->Close();