void plotEloss(TString file, int nEvents=-1) {
 
  gStyle->SetPalette(1);
  gROOT->SetStyle("Plain");
  
  TFile* inFile = new TFile(file, "read");
  TTree* tree = inFile->Get("cbmsim");
  if(tree==NULL) {
    std::cout<<"Could not get tree 'cbmsim' ... aborting!"<<std::endl;
    return;
  }

  int nEv = tree->GetEntries();
  std::cout<<"Tree has "<<nEv<<" entries..."<<std::endl;
  int nE;
  if(nEvents<0 || nEvents>nEv)
    nE = nEv;
  else
    nE = nEvents;
  std::cout<<"nE: "<<nE<<std::endl;
  
  TClonesArray* arr = new TClonesArray("TpcPoint");
  tree->SetBranchAddress("TpcPoint",&arr);
  
  TH1D* edepDist = new TH1D("edepDist", "TpcPoint energy loss distribution",1000,0,200*1.E-9);
  TH1D* stepDist = new TH1D("stepDist", "Step length distribution",1000,0,1);
  TH1D* dedxDist = new TH1D("dedxDist", "dE/dx distribution",2000,0,10*1.E-6);
  TH2D* dedxVsStep = new TH2D("dedxVsStep", "dE/dx vs. Setp",1000,0,1,2000,0,10*1.E-6);
  TH1D* posR = new TH1D("posR","Radial TpcPoint Positions", 1000,14.5,42.);
  TH1D* posZ = new TH1D("posZ","TpcPoint Z Positions", 1000,-45.,115.);
  
    
  for(unsigned int ie=0; ie<nE; ie++) {
    tree->GetEntry(ie);
    unsigned int npoints = arr->GetEntriesFast();
    for(unsigned int ip=0; ip<npoints; ip++) {
      TpcPoint* p = (TpcPoint*)(*arr)[ip];
      TVector3 pos;
      p->Position(pos);
      posR->Fill(pos.Perp());
      posZ->Fill(pos.Z());
      double eloss = p->GetEnergyLoss();
      double step = p->GetLength();
      edepDist->Fill(eloss);
      stepDist->Fill(step);
      dedxDist->Fill(eloss/step);
      dedxVsStep->Fill(step,eloss);
    }
  }

  TCanvas* c = new TCanvas();
  c->Divide(2,1);
  c->cd(1);
  edepDist->Draw();
  c->cd(2);
  stepDist->Draw();
  TCanvas* c2 = new TCanvas();
  dedxDist->Draw();
  TCanvas* c3 = new TCanvas();
  dedxVsStep->Draw("colz");
  TCanvas* c4 = new TCanvas();
  c4->Divide(2,1);
  c4->cd(1);
  posR->Draw();
  c4->cd(2);
  posZ->Draw();
    
    
  
  
  
  
}