Double_t BrFdstMainSelector::GetDetectorEfficiency(const TString& detector, const Float_t& x,
						   const Float_t& y, const Float_t& z) 
{
  // Return detector efficiency for the specified detector. 
  // For each detector there are three parameters that determine the efficiency. For the RICH
  // x, y and z correspond to centrality, gamma and x slope, respectively. For the other detectors, 
  // they correspond to centrality, x position and x slope, respectively.

  // Define local variables.
  TH3F *hEff, *hRef;
  TString det = detector;
  det.ToUpper();
  Double_t histX = x;
  Double_t histY = y;
  Double_t histZ = z;
  
  // Special setting which needs extra care.
  TRegexp specialSetting("12_.1692");

  // Determine which detector and assign the right histograms to work with.
  Int_t minRefCont = 5;
  if (det == "T1") { 
    hEff = fHEffT1; 
    hRef = fHRefT1; 
  }
  else if (det == "T2") { 
    hEff = fHEffT2; 
    hRef = fHRefT2;
  }  
  else if (det == "T3") { 
    hEff = fHEffT3; 
    hRef = fHRefT3;
  }
  else if (det == "T4") {
    hEff = fHEffT4;
    hRef = fHRefT4;
    if (fSetting.Contains(specialSetting))
      minRefCont = 4;
  }
  else if (det == "T5") {
    hEff = fHEffT5;
    hRef = fHRefT5;
    if (fSetting.Contains(specialSetting))
      minRefCont = 4;
  }
  else if (det == "H1") {
    hEff = fHEffH1;
    hRef = fHRefH1;
  }
  else if (det == "H2") {
    hEff = fHEffH2;
    hRef = fHRefH2;
  }
  else if (det == "RICH") {
    hEff = fHEffRich;
    hRef = fHRefRich;
    histY = TMath::Min(histY, 100.); // Assign maximum gamma for RICH.
    minRefCont = 10;
  }
  else {
    Error("GetDetectorEfficiency", "Unknown detector %s.", detector.Data());
    return 0.;
  }

  // Find which histogram bin corresponds to the specified parameters, and 
  // the ref histogram content for this bin.
  const Int_t currBin = hRef->FindBin(histX, histY, histZ);
  Int_t currRefCont = (Int_t) hRef->GetBinContent(currBin);

  // Define efficiency.
  Double_t eff = 0.;

  // Return efficiency if the it is defined for this bin
  if (currRefCont > minRefCont)
    return (Double_t) hEff->GetBinContent(currBin);
  
  // Efficiency is not defined for this bin so we should find the closest bin with
  // defined value.
  Int_t xBin = hRef->GetXaxis()->FindBin(histX);
  Int_t yBin = hRef->GetYaxis()->FindBin(histY);
  Int_t zBin = hRef->GetZaxis()->FindBin(histZ);
  
  Int_t iR = 0; 		// Current radius, starting at 0.
  do {
    iR++;
    
    // Loop over all y bins within current radius.
    for (Int_t iY = yBin - iR; iY <= yBin + iR; iY++) {
      if (iY < 1 || iY > hRef->GetNbinsY()) 
	continue;	// Outside axis' range.
    
      // Loop over all z bins within current radius.
      for (Int_t iZ = zBin - iR; iZ <= zBin + iR; iZ++) {
	if (iZ < 1 || iZ > hRef->GetNbinsZ()) 
	  continue; // Outside axis' range.

	Float_t radius = TMath::Sqrt((Float_t)((iY - yBin) * (iY - yBin) + 
					       (iZ - zBin) * (iZ - zBin)));

	if (Float_t(iR) > radius) 
	  currRefCont = (Int_t) hRef->GetBinContent(xBin, iY, iZ);

	if (currRefCont > minRefCont)
	  eff = (Double_t) hEff->GetBinContent(xBin, iY, iZ);

	if (eff)
	  break;
      }

      if (eff)
	break;
    }
  } while (!eff && (iR < hRef->GetNbinsY()) && (iR < hRef->GetNbinsZ()));
  
  // Send warning if no efficiency was found.
  if (!eff)
    if (det == "RICH")
      Warning("GetDetectorEfficiency", 
	      "Could not find efficiency in %s:\tcentrality = %f,\tgamma = %f,\tx slope = %f",
	      hEff->GetName(), x, y, z);
    else
      Warning("GetDetectorEfficiency", 
	      "Could not find efficiency in %s:\tcentrality = %f,\tx position = %f,\tx slope = %f",
	      hEff->GetName(), x, y, z);
  
  return eff;
}