double onebin;

Double_t gausPeak(Double_t *x, Double_t *par) {
  //return par[0]/sqrt(2.0*TMath::Pi()*par[2]*par[2])
  //*exp(-(x[0]-par[1])*(x[0]-par[1])/(2.0 * par[2] * par[2]));
  return par[0]*exp(-(x[0]-par[1])*(x[0]-par[1])/(2.0 * par[2] * par[2]));
  //return (onebin*par[0]*par[1])/(2.0*TMath::Pi())/
  //TMath::Max(1.e-10, (x[0]-par[2])*(x[0]-par[2]) + 0.25*par[1]*par[1]);
}

Double_t background(Double_t *x, Double_t *par) {
  return par[0] + par[1]*x[0] + par[2]*x[0]**2 + par[3]*x[0]**3;
  //return par[0] + par[1]*x[0] + par[2]*x[0]**2;
} 

Double_t fitFunction(Double_t *x, Double_t *par) {
  return background(x,par) + gausPeak(x, &par[4]);
}
void fitGausBack(TH1F *h1)
{
  //onebin=(1.6-1.5)/(h1->GetXaxis()->FindBin(1.6)-h1->GetXaxis()->FindBin(1.5));

  TF1 *fitFcn = new TF1("fitFcn", fitFunction, 1.1, 1.25, 7);
  TF1 *backFcn = new TF1("backFcn", background, 1.1, 1.25, 4);
  TF1 *signalFcn = new TF1("signalFcn", gausPeak, 1.1, 1.25, 4);

  h1->Fit("backFcn","","",1.1,1.2);

  //fitFcn->SetParameter(0, -5.6e+6);
  //fitFcn->SetParameter(1, 1.07e+7);
  //fitFcn->SetParameter(2, -6.8e+6);
  //fitFcn->SetParameter(3, 1.45e+6);
  fitFcn->SetParameter(0, backFcn->GetParameter(0));
  fitFcn->SetParameter(1, backFcn->GetParameter(1));
  fitFcn->SetParameter(2, backFcn->GetParameter(2));
  fitFcn->SetParameter(3, backFcn->GetParameter(3));
  fitFcn->SetParameter(4, 40);
  fitFcn->SetParameter(5, 1.21);
  fitFcn->SetParameter(6, 0.01);
  
  h1->Fit("fitFcn","","",1.1,1.25);

  backFcn->SetParameter(0, fitFcn->GetParameter(0));
  backFcn->SetParameter(1, fitFcn->GetParameter(1));
  backFcn->SetParameter(2, fitFcn->GetParameter(2));
  backFcn->SetParameter(3, fitFcn->GetParameter(3));
  backFcn->Draw("same");
  signalFcn->SetParameter(0, fitFcn->GetParameter(4));
  signalFcn->SetParameter(1, fitFcn->GetParameter(5));
  signalFcn->SetParameter(2, fitFcn->GetParameter(6));
  signalFcn->Draw("same");
  double mean, width;
  double x1,x2;
  int    bin1, bin2;
  int    n;
  double probability;
  double    sigma;

  sigma = 3.0;

  width = fitFcn->GetParameter(5);
  mean = fitFcn->GetParameter(6);

  x1 = mean - sigma*width/2.0;
  x2 = mean + sigma*width/2.0;

  bin1 = h1->GetXaxis()->FindBin(x1);
  bin2 = h1->GetXaxis()->FindBin(x2);

  n = h1->Integral(bin1, bin2);
  //probability = (double)n/(double)h1->GetEntries();

  //printf("n=%d pro=%f\n", n, probability);
  
  TLine *l1 = new TLine(x1, 0, x1, 20000);
  TLine *l2 = new TLine(x2, 0, x2, 20000);
  l1->SetLineColor(kRed);
  l2->SetLineColor(kRed);
  l1->Draw("same");
  l2->Draw("same");

}