void PID_paper(double gamma, int start= 1){
  
  TFile * f1 = new TFile("pid_total.root");
  TH2F * hPID = (TH2F*) f1->Get("hPID2");
  
  gStyle->SetOptStat("");  /// no state
  gStyle->SetOptTitle(0);  /// no title
  
  TCanvas * ccc = new TCanvas("ccc", "ccc", 1000, 1000);
  ///ccc->Divide(2,1);
  
  ///========= set Z-color
  
  ///---- custom color
  ///Int_t colors[] = {0, 1, 2, 3, 4, 5, 6}; 
  ///gStyle->SetPalette((sizeof(colors)/sizeof(Int_t)), colors);
  
  
  ///----- build-in color
  int color = kBeach;  
  //int color = kGreenBrownTerrain;  
  //int color = kColorPrintableOnGrey;
  //int color = kSunset;
  
  ///gStyle->SetPalette(kBlueRedYellow);
  ///gStyle->SetPalette(kRainBow);
  gStyle->SetPalette(color);TColor::InvertPalette();
  
  ///======== set contours
    
  TGraph * ggg = new TGraph(); /// this is for displaying the gamma correction
  
  const int nCon = 200;  /// number of contours
  double contours[nCon];
  
  double zMax = hPID->GetMaximum();
  
  for( int i = 0; i < nCon; i++){
    double xpos = i*1.0/nCon;
    double ypos = TMath::Power(xpos, gamma) *0.95;
    
    contours[i] = start + ypos*(zMax - start);
    ggg->AddPoint(xpos, ypos); 
  }
    
  ccc->cd();ccc->cd()->SetGrid(0,0);
  hPID->GetYaxis()->SetRangeUser(1.5, 16);
  hPID->SetContour(nCon, contours);
  hPID->Draw("col");
  
  TEllipse * si42 = new TEllipse(3.01, 14, 0.05, 0.55);
  si42->SetFillStyle(0);
  si42->SetLineColor(2);
  si42->SetLineWidth(3);
  
  si42->Draw("same");
  
  TLatex text;
  text.SetTextColor(2);
  text.SetTextSize(0.05);
  text.DrawLatex(3.05, 14.2, "^{42}Si");

  ///------ in case want to see the gamma correction
  ///ccc->cd(2); 
  ///ggg->Draw("AP*");
  
  ///====== save as pdf
  ccc->SaveAs(Form("haha_%3.1f_%d_%d.pdf", gamma, start, color));


}