Changes between Version 6 and Version 7 of WorkBook/QuickTour

Timestamp:

Nov 22, 2012, 9:13:48 AM (12 years ago)

Author:

Pavel Demin

Comment:

--

WorkBook/QuickTour

@@ -55 +55 @@
 }}}
 
+== 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 [wiki:WorkBook/RootTreeDescription]
+
+
+=== Macro-based analysis ===
+
+Delphes/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)
+{
+  // 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
+      TRootJet *jet = (TRootJet*) branchJet->At(0);
+      
+      // Plot jet transverse momentum
+      histJetPT->Fill(jet->PT);
+      
+      // Print jet transverse momentum
+      cout << jet->PT << endl;
+    }
+
+    TRootElectron *elec1, *elec2;
+    TLorentzVector vec1, vec2;
+
+    // If event contains at least 2 electrons
+    if(branchElectron->GetEntries() > 1)
+    {
+
+      // Take first two electrons
+      elec1 = (TRootElectron *) branchElectron->At(0);
+      elec2 = (TRootElectron *) branchElectron->At(1);
+
+      // Create two 4-vectors for the electrons
+      vec1.SetPtEtaPhiM(elec1->PT, elec1->Eta, elec1->Phi, 0.0);
+      vec2.SetPtEtaPhiM(elec2->PT, elec2->Eta, elec2->Phi, 0.0);
+
+      // Plot their invariant mass
+      histMass->Fill((vec1 + vec2).M());
+    }
+  }
+
+  // Show resulting histograms
+  histJetPT->Draw();
+  histMass->Draw();
+}
+}}}
+
+=== More advanced macro-based analysis ===
+
+Delphes/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.
+
+Here are commands to run this macro:
+{{{
+root
+gSystem->Load("libDelphes");
+.X examples/Example2.C("delphes_output.root");
+}}}
+
+
+