Delphes is a C++ framework, performing a fast multipurpose detector response simulation.
More details can be found on the Delphes website https://delphes.github.io
Commands to get the code:
wget http://cp3.irmp.ucl.ac.be/downloads/Delphes-3.5.0.tar.gz
tar -zxf Delphes-3.5.0.tar.gz
Commands to compile the code:
cd Delphes-3.5.0
make
Finally, we can run Delphes:
./DelphesHepMC3
Command line parameters:
./DelphesHepMC3 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.
Let's simulate some Z->ee events:
wget http://cp3.irmp.ucl.ac.be/downloads/z_ee.hep.gz
gunzip z_ee.hep.gz
./DelphesSTDHEP cards/delphes_card_CMS.tcl delphes_output.root z_ee.hep
or
curl -s http://cp3.irmp.ucl.ac.be/downloads/z_ee.hep.gz | gunzip | ./DelphesSTDHEP cards/delphes_card_CMS.tcl delphes_output.root
For more detailed documentation, please visit https://delphes.github.io/workbook
git clone https://github.com/delphes/delphes Delphes
cd Delphes
source /cvmfs/sft.cern.ch/lcg/views/LCG_105/x86_64-el9-gcc12-opt/setup.sh
make
Delphes is also available as a pre-built binary package from conda-forge.
The scripts used to build this package are available at
https://github.com/conda-forge/delphes-feedstock
Command to install the package in a conda environment:
conda install --channel conda-forge delphes
Commands to run the Z->ee example from the 'Quick start' section above in a conda environment:
wget http://cp3.irmp.ucl.ac.be/downloads/z_ee.hep.gz
gunzip z_ee.hep.gz
DelphesSTDHEP $CONDA_PREFIX/cards/delphes_card_CMS.tcl delphes_output.root z_ee.hep
where the CONDA_PREFIX environment variable is automatically set when the conda environment is activated.
The cards and examples directories from this repository are also installed under $CONDA_PREFIX.
Now we can start ROOT and look at the data stored in the output ROOT file.
Start ROOT and load Delphes shared library:
root -l
gSystem->Load("libDelphes");
Open ROOT file and do some basic analysis using Draw or TBrowser:
TFile *f = TFile::Open("delphes_output.root");
f->Get("Delphes")->Draw("Electron.PT");
TBrowser browser;
Notes:
Delphesis the tree name. It can be learned e.g. from TBrowser.Electronis the branch name.PTis a variable (leaf) of this branch.
Complete description of all branches can be found in doc/RootTreeDescription.html.
This information is also available at this link.
Analysis macro consists of histogram booking, event loop (histogram filling), histogram display.
Start ROOT and load Delphes 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 *branchElectron = treeReader->UseBranch("Electron");
// Book histograms
TH1 *histElectronPT = new TH1F("electron pt", "electron P_{T}", 50, 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 electron
if(branchElectron->GetEntries() > 0)
{
// Take first electron
Electron *electron = (Electron*) branchElectron->At(0);
// Plot electron transverse momentum
histElectronPT->Fill(electron->PT);
// Print electron transverse momentum
cout << electron->PT << endl;
}
}
// Show resulting histograms
histElectronPT->Draw();
}
The examples directory contains ROOT macros Example1.C, Example2.C and Example3.C.
Here are the commands to run these ROOT macros:
root -l
.X examples/Example1.C("delphes_output.root");
or
root -l examples/Example1.C'("delphes_output.root")'