Changes in README_4LHCb [2b01e13:be386ff] in git

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• README_4LHCb (modified) (2 diffs)

README_4LHCb

@@ -50 +50 @@
 2) Simulate p p -> b b~ events 
 
-
-  wget http://cp3.irmp.ucl.ac.be/downloads/pp2bb.hep.tgz
   tar -xzvf pp2bb.hep.tgz
   ./DelphesSTDHEP examples/delphes_card_prelLHCb.tcl delphes_output.root pp2bb.hep
@@ -61 +59 @@
 
 
+
+Simple analysis using TTree::Draw
+=================================
+
+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::Open("delphes_output.root");
+   Delphes->Draw("Track.PT");
+   TBrowser browser;
+
+Note 1: Delphes - tree name, it can be learned e.g. from TBrowser
+
+Note 2: Track - branch name; PT - variable (leaf) of this branch
+
+Complete description of all branches can be found in
+
+   doc/RootTreeDescription.html
+
+This information is also available at
+
+   https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook/RootTreeDescription
+
+
+Macro-based analysis
+====================
+
+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 *branchTrack = treeReader->UseBranch("Track");
+
+  // Book histograms
+  TH1 *histTrackPT = new TH1F("track pt", "track P_{T}", 50, 0.0, 20.0);
+
+  // 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 track
+    if(branchTrack->GetEntries() > 0)
+    {
+      // Take first track
+      Track *track = (Track*) branchTrack->At(0);
+      
+      // Plot track transverse momentum
+      histTrackPT->Fill(track->PT);
+      
+      // Print electron transverse momentum and Particle Data Group ID
+      cout << track->PID<< "   " << track->PT << endl;
+    }
+
+  }
+
+  // Show resulting histograms
+  histTrackPT->Draw();
+}
+