Installing Delphes from Source

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

• ​ROOT Data Analysis Framework
• ​Tcl scripting language

Commands to download Delphes' source and build Delphes:

setup ROOT environment variables

wget http://cp3.irmp.ucl.ac.be/downloads/Delphes-3.0.6.tar.gz
tar -zxf Delphes-3.0.6.tar.gz

cd Delphes-3.0.6
make -j 4

Running Delphes

When running Delphes without parameters or when supplying an invalid command line, the following message will be shown:

./DelphesHepMC
 Usage: DelphesHepMC config_file output_file [input_file(s)]
 config_file - configuration file in Tcl format,
 output_file - output file in ROOT format,
 input_file(s) - input file(s) in HepMC format,
 with no input_file, or when input_file is -, read standard input.

Running Delphes with HepMC input files:

./DelphesHepMC examples/delphes_card_CMS.tcl output.root input.hepmc

Running Delphes with STDHEP (XDR) input files:

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

Running Delphes with LHEF input files:

./DelphesLHEF examples/delphes_card_CMS.tcl delphes_output.root input.lhef

Running Delphes with files stored in CASTOR:

rfcat /castor/cern.ch/user/d/demine/test.hepmc.gz | gunzip | ./DelphesHepMC examples/delphes_card_CMS.tcl delphes_output.root

Running Delphes with files accessible via HTTP:

curl http://cp3.irmp.ucl.ac.be/~demin/test.hepmc.gz | gunzip | ./DelphesHepMC examples/delphes_card_CMS.tcl delphes_output.root

Analyzing Delphes' Output

Delphes' output can be analyzed with the ROOT data analysis framework.

Simple analysis using TTree::Draw

Start ROOT and load Delphes' shared library:

root
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 at WorkBook/RootTreeDescription

Macro-based analysis

The examples directory contains a basic ROOT analysis macro called Example1.C. This ROOT analysis macro consists of histogram booking, event loop (histogram filling), histogram display.

Here are commands to run this macro:

root
gSystem->Load("libDelphes");
.X examples/Example1.C("delphes_output.root");

And here is the full source code of this macro:

void Example1(const char *inputFile)
{
  gSystem->Load("libDelphes");

  // Create chain of root trees
  TChain chain("Delphes");
  chain.Add(inputFile);
  
  // 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");
  TClonesArray *branchElectron = treeReader->UseBranch("Electron");
  
  // Book histograms
  TH1 *histJetPT = new TH1F("jet_pt", "jet P_{T}", 100, 0.0, 100.0);
  TH1 *histMass = new TH1F("mass", "M_{inv}(e_{1}, e_{2})", 100, 40.0, 140.0);

  // 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;
    }

    Electron *elec1, *elec2;

    // If event contains at least 2 electrons
    if(branchElectron->GetEntries() > 1)
    {
      // Take first two electrons
      elec1 = (Electron *) branchElectron->At(0);
      elec2 = (Electron *) branchElectron->At(1);

      // Plot their invariant mass
      histMass->Fill(((elec1->P4()) + (elec2->P4())).M());
    }
  }

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

More advanced macro-based analysis

The examples directory contains a ROOT macro called Example2.C demonstrating how to use class ExRootTreeReader to access data and class ExRootResult to manage histograms booking and output.

This macro can be run with the following command:

root -l examples/Example2.C\(\"delphes_output.root\"\)