// int roomodel(){
//     RooRealVar x ("x","observable",-10,15);
//     RooRealVar mean("mean","mean of the dist",5.4,"GeV");
//     RooRealVar sigma("sigma","std deviaton",2);

//     RooGaussian model("model","our pdf",x,mean,sigma);
//     // creating a empty plot frame
//     RooPlot* xframe = x.frame();
//     model.plotOn(xframe);
//     xframe->Draw();
// }
// #include"TF1.h"
using namespace RooFit;
//   double ROOT::Math::chisquared_cdf_c	(	double 	x,
// double 	r,
// double 	x0 = 0 
// )		;
void roomodel(){
TFile *myfile =new TFile("sel_BsToPhiMuMu_OfficialMC_signal_2016Mini_Presel_v2_mc.lite_cut_bdt_s86000000.root","READ");
TTree *mytree =(TTree*)myfile->Get("tree"); //we want to read out the tree,so we have to make a reeference
double Bmassi;
mytree->SetBranchAddress("Bmass",&Bmassi);

int entries = mytree->GetEntries();
cout<<entries<<endl;
TH1F *hist = new TH1F("hist","Bmass",200,4.6,5.7);

for (int i=0;i<entries;i++){
    mytree->GetEntry(i);
    // cout<<Bmass<<endl;
    hist->Fill(Bmassi);
}
RooRealVar x("x", "x", 4.6,5.7);
RooDataHist dh("dh", "dh", x, Import(*hist));
 RooPlot *frame = x.frame();
   dh.plotOn(frame);
   RooRealVar mean("mean", "mean", 0, 0, 10);
   RooRealVar sigma("sigma", "sigma", 3, 0.001, 10);
   RooGaussian gauss("gauss", "gauss", x, mean, sigma);
   gauss.fitTo(dh,"R");
   gauss.plotOn(frame);
   frame->Draw();
}