void r3btra(Int_t nEvents = 1)
{
  
  TString dir = getenv("VMCWORKDIR");
  TString r3bdir = dir + "/macros";

  TString r3b_geomdir = dir + "/geometry";
  gSystem->Setenv("GEOMPATH",r3b_geomdir.Data());

  TString r3b_confdir = dir + "gconfig";
  gSystem->Setenv("CONFIG_DIR",r3b_confdir.Data());

// Output files
  TString OutFile = "r3bsim.root";
  TString ParFile = "r3bpar.root";


  // In general, the following parts need not be touched
  // ========================================================================

  // ----    Debug option   -------------------------------------------------
  gDebug = 0;
  // ------------------------------------------------------------------------

  // -----   Timer   --------------------------------------------------------
  TStopwatch timer;
  timer.Start();
  // ------------------------------------------------------------------------

  // ----  Load libraries   -------------------------------------------------
  gROOT->LoadMacro("$VMCWORKDIR/gconfig/basiclibs.C");
  basiclibs();
  gSystem->Load("libGeoBase");
  gSystem->Load("libParBase");
  gSystem->Load("libBase");
  gSystem->Load("libMCStack");
  gSystem->Load("libField");
  gSystem->Load("libGen");

  //----  Load R3B specific libraries ---------------------------------------
  gSystem->Load("libR3Bbase");
  gSystem->Load("libR3BPassive");
  gSystem->Load("libR3BData");
  gSystem->Load("libR3BCal");
  gSystem->Load("libR3BCalo");
  gSystem->Load("libR3BDch");
  gSystem->Load("libR3BGfi");
  gSystem->Load("libR3BLand");
  gSystem->Load("libR3BmTof");
  gSystem->Load("libR3BTof");
  gSystem->Load("libR3BTra");

 
  // -----   Create simulation run   ----------------------------------------
  FairRunSim* run = new FairRunSim();
  run->SetName("TGeant3");              // Transport engine
  run->SetOutputFile(OutFile.Data());          // Output file
  FairRuntimeDb* rtdb = run->GetRuntimeDb();
  
  // -----   Create media   -------------------------------------------------
  run->SetMaterials("media_r3b.geo");       // Materials
  
  // -----   Create R3B geometry --------------------------------------------


  //R3B Cave definition
  FairModule* cave= new R3BCave("CAVE");
  cave->SetGeometryFileName("r3b_cave.geo");
  run->AddModule(cave);

  //R3B Target definition
  FairModule* target= new R3BTarget("LeadTarget");
  run->AddModule(target);

  //R3B Magnet definition
  FairModule* mag = new R3BMagnet("AladinMagnet");
  run->AddModule(mag);

  // Tracker
  FairDetector* tra = new R3BTra("Tracker", kTRUE);
  Double_t fCutOffSi = 1.0e-06;  // Cut-Off -> 10KeV only in Si
  ((R3BTra*) tra)->SetEnergyCutOff(fCutOffSi);
  run->AddModule(tra);


  // DCH drift chambers
   FairDetector* dch = new R3BDch("Dch", kTRUE);
   run->AddModule(dch);

   // Tof
  FairDetector* tof = new R3BTof("Tof", kTRUE);
  Double_t fCutOffSci = 1.0e-05;  // Cut-Off -> 10.KeV only in Sci.
  ((R3BTof*) tof)->SetEnergyCutOff(fCutOffSci);
  run->AddModule(tof);

  // mTof
  FairDetector* mTof = new R3BmTof("mTof", kTRUE);
  ((R3BmTof*) mTof)->SetEnergyCutOff(fCutOffSci);
  run->AddModule(mTof);


  // -----   Create magnetic field   ----------------------------------------
  Int_t typeOfMagneticField = 0;
  Int_t fieldScale = 1;
//  Bool_t fVerbose = kTRUE;
  Bool_t fVerbose = kFALSE;

  R3BFieldMap* magField = new R3BFieldMap(typeOfMagneticField,fVerbose);
  magField->SetPosition(0., 0., 0.);
  magField->SetScale(fieldScale);
  run->SetField(magField);



  // -----   Create PrimaryGenerator   --------------------------------------
  FairPrimaryGenerator* primGen = new FairPrimaryGenerator();

  Double_t pdgId=211; // pion beam
  Double_t theta1= 0.;  // polar angle distribution
  Double_t theta2= 7.;
  Double_t momentum=.8; // 10 GeV/c
  FairBoxGenerator* boxGen = new FairBoxGenerator(pdgId, 50);
  boxGen->SetThetaRange (   theta1,   theta2);
  boxGen->SetPRange     (momentum,momentum*2.);
  boxGen->SetPhiRange   (0.,360.);
  boxGen->SetXYZ(0.0,0.0,-1.5);
  primGen->AddGenerator(boxGen);

  run->SetGenerator(primGen);



  //-------Set visualisation flag to true------------------------------------
  run->SetStoreTraj(kTRUE);

  // -----   Initialize simulation run   ------------------------------------
  run->Init();

  // ------  Increase nb of step for CALO
  Int_t nSteps = -15000;
  gMC->SetMaxNStep(nSteps);

  // -----   Runtime database   ---------------------------------------------
  Bool_t kParameterMerged = kTRUE;
  FairParRootFileIo* parOut = new FairParRootFileIo(kParameterMerged);
  parOut->open(ParFile.Data());
  rtdb->setOutput(parOut);
  rtdb->saveOutput();
  rtdb->print();
   


  // -----   Start run   ----------------------------------------------------
  run->Run(10);
  
  // -----   Finish   -------------------------------------------------------
  timer.Stop();
  Double_t rtime = timer.RealTime();
  Double_t ctime = timer.CpuTime();
  cout << endl << endl;
  cout << "Macro finished succesfully." << endl;
  cout << "Output file is "    << OutFile << endl;
  cout << "Parameter file is " << ParFile << endl;
  cout << "Real time " << rtime << " s, CPU time " << ctime 
       << "s" << endl << endl;
  // ------------------------------------------------------------------------

  cout << " Test passed" << endl;
  cout << " All ok " << endl;

}