double Integral(TH1F* Hist, double xmin1, double xmax1){
    
    TAxis *axis = Hist->GetXaxis();
    int bmin1 = axis->FindBin(xmin1);
    int bmax1 = axis->FindBin(xmax1);
    double integral1 = Hist->Integral(bmin1,bmax1);
    return integral1;
}



void poisson(){

    TFile *f3 = new TFile("Med0_04GeV_4Quartz2000Ev10MCell.root");
    f3->ls();
    TH1F * h3 = (TH1F*)f3->Get("ParCell");
    //gStyle->SetOptStat(1100);
    gStyle->SetOptFit(1);
    TCanvas* c2= new TCanvas("c2"," ",900,900);

    h3->Draw();

    int integral0 = Integral(h3, -10, 60);
   
    int integral1 = Integral(h3, 1050, 1600);

    int integral2 = Integral(h3, 2400, 3200);

    int integral3 = Integral(h3, 3800, 4650);

    int integral4 = Integral(h3, 4800, 6050);

    int integral5 = Integral(h3, 6800, 7500);
  
    int integral6 = Integral(h3, 8400, 9000);
    
    int integral7 = Integral(h3, 9900, 10400);

    TH2F * hn = new TH2F("hn", "",10, 0,10, 1000, 0, 5000);

    int sum = integral0 +integral1 +integral2 +integral3 +integral4 +integral5 +integral6 +integral7;

    int a0 = 0;
    int a1 = 1;
    int a2 = 2;
    int a3 = 3;
    int a4 = 4;
    int a5 = 5;
    int a6 = 6;
    int a7 = 7;
    
    
    hn->Fill(a0, integral0);
    hn->Fill(a1, integral1);
    hn->Fill(a2, integral2);
    hn->Fill(a3, integral3);
    hn->Fill(a4, integral4);
    hn->Fill(a5, integral5);
    hn->Fill(a6, integral6);
    hn->Fill(a7,integral7);

    hn->SetMarkerStyle(20);
    hn->SetMarkerSize(0.5);

    TCanvas* c3= new TCanvas("c3"," ",900,900);

    TF1 *fit = new TF1("fit","[0]*TMath::Poisson(x,[1])",0,8);
    //TF1 *fit = new TF1("fit","gaus",0,8);
    //TF1 *fit = new TF1("fit","(  (TMath::Exp(-[1]) * TMath::Power([1],x) ) / TMath::Gamma(x+1.0))",0.1,7);
    hn->Fit("fit");
    hn->Draw();
}