void runMC(Int_t field, TString gas, Int_t gain, TString outdir="./", int nEvents=5000, Int_t run = 1, unsigned int seed=4711) {

  // ------------------------------------------------------------------------
  gRandom->SetSeed(seed);
  //gROOT->ProcessLine(".x $VMCWORKDIR/gconfig/rootlogon.C");
  // ========================================================================
  // Verbosity level (0=quiet, 1=event level, 2=track level, 3=debug)
  Int_t iVerbose = 1;
  FairRunSim *fRun = new FairRunSim();
  
  // set the MC version used
  // --------------------------------------------------
  TString mcMode = "TGeant3";
  fRun->SetName(mcMode);

  TString jobdir=outdir;
  int length = jobdir.Length();
  if(jobdir[length-1] != "/")
    jobdir.Append("/");
  
  TString jobname=Form("Cosmics_FopiMC_%i%s%i_%i.mc.root",field,gas.Data(),gain,run);
  
  TString outfile = jobdir+jobname;
  std::cout<<outfile<<std::endl;
  fRun->SetOutputFile(outfile);
  std::cout<<"Set output file to "<<outfile<<std::endl;

  TString copy = outfile;
  TString parfile = copy.ReplaceAll("mc.root","param.root");
  TString digifile = gSystem->Getenv("VMCWORKDIR");
  digifile += Form("/tpc/FOPI/par/tpc.%i%s%iMC_long.par",field,gas.Data(),gain);
  cout<<digifile<<endl;
  //  char bufferGas[2];
  //  sprintf(bufferGas,"%s",gas);
  //  digifile += bufferGas;
  //  dififile += "_";
  //  char bufferField[

  FairRuntimeDb *rtdb=fRun->GetRuntimeDb();
  FairParAsciiFileIo* parIo1 = new FairParAsciiFileIo();
  parIo1->open(digifile.Data(),"in");
  rtdb->setFirstInput(parIo1);
  Bool_t kParameterMerged=kTRUE;

  FairParRootFileIo* parOut=new FairParRootFileIo(kParameterMerged);
  parOut->open(parfile.Data());
  rtdb->setOutput(parOut);
  
  TpcDigiPar* par = (TpcDigiPar*) rtdb->getContainer("TpcDigiPar");
  par->setInputVersion(fRun->GetRunId(),1);
  par->setChanged(kTRUE);
  par->init();
  //================================================================================
  // build a run specific geometry
  // run the FopiGeom.C in a separate root session
  //
  // taroff: distance between target and center of magnet
  // targetpos: distance between real target position and nominal FOPI target
  // position
  // In experiment S339 the distance between the nominal FOPI target position
  // and the center of the magnet is 41 cm.
 /* Double_t taroff = -65;
  Double_t targetpos = taroff+41.;
  // possible materials: copper (default), lead, carbon
  TString targetmat = TString("copper");
  TString alignmentFileName = par->getAlignmentFile();
  TString geoFile;
  geoFile.Form("$VMCWORKDIR/geometry/FopiGeom_s339%5.1f.root",targetpos);
  TString geoFileName;
  geoFileName.Form("FopiGeom_s339%5.1f.root",targetpos);
  TString cmd;
  cmd.Form(".! root -b -q '$FOPI2ROOT/fopigeometry/FopiGeom.C(%f,\"%s\",\"%s\",\"%s\",kFALSE,kFALSE)'",targetpos,targetmat.Data(),alignmentFileName.Data(),geoFile.Data());
  gROOT->ProcessLine(cmd);*/

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

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


  // Set Material file Name
  //-----------------------
  fRun->SetMaterials("media_pnd.geo");
  
  // Create and add detectors
  //-------------------------
  // FairModule *Cave= new FopiDetector("FOPI");
  // Cave->SetGeometryFileName(geoFile);
  // fRun->AddModule(Cave);

  FairModule *Cave= new PndCave("CAVE");
  Cave->SetGeometryFileName("pndcave.geo");
  fRun->AddModule(Cave);

  TpcDetector *Tpc = new TpcDetector("TPC", kTRUE);
  Tpc->SetGeometryFileName("tpc_prototype_long_ArCO2.root");
  Tpc->SetMixture("TPCFOPI_mix"); // TPCmixture: Neon CO2 (90/10); TPCFOPI_mix: Ar/CO2 (90/10)
  if(mcMode=="TGeant3") Tpc->SetAliMC();
  fRun->AddModule(Tpc);

  
  FairPrimaryGenerator* primGen = new FairPrimaryGenerator();
  fRun->SetGenerator(primGen);

  FairBoxGeneratorMOD* boxGen = new FairBoxGeneratorMOD(13,1);
  //boxGen->SetDebug(kTRUE);
  boxGen->SetPRange(2,2); // GeV/c
  boxGen->SetPhiRange(270.,270.); // Azimuth angle range [degree]
  boxGen->SetThetaRange(90.,90.); // Polar angle in lab system range [degree]
  boxGen->SetBoxXYZ(-17,17, 17,17, -65, 440);
  primGen->AddGenerator(boxGen);

  
  // Create and Set Magnetic Field
  // --------------------
  // Constant Field
  PndConstField *fMagField=new PndConstField();
  fMagField->SetField(0., 0. , 6. ); // values are in kG
  fMagField->SetFieldRegion(-17, 17,  -17, 17, -2000, 2000); // values are in cm
  fRun->SetField(fMagField);
   
  /**Initialize the session*/
  fRun->Init();
  // Initialize the Digimapper:
  // TpcDigiPar* tpcpar = FairRun::Instance()->GetRuntimeDb()->getContainer("TpcDigiPar");
  // TpcDigiMapper::getInstance()->init(tpcpar);
  // //TpcDigiMapper::getInstance()->forceManualDriftVel(forceDriftVel);
  // TpcAlignmentManager::init(tpcpar->getAlignmentFile());
  rtdb->saveOutput();
  rtdb->print();

  // Transport nEvents
  // -----------------
  fRun->Run(nEvents);


  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;
  cout << endl;
  // ------------------------------------------------------------------------


}