{
    using namespace RooFit;
    
    TFile *fin = new TFile("example_data.root");
    TNtupleD* nt = (TNtupleD *)fin->Get("nt");
    
    RooRealVar mass("mass","mass",0.,2.);
    RooDataSet data("data","data",nt,RooArgSet(mass));
    
    RooRealVar mu("mu","mu",1.0,0.5,1.5);
    RooRealVar sigma("sigma","sigma",0.05,0.001,0.15);
    RooGaussian gaus("gaus","gaus",mass,mu,sigma);
    RooRealVar slope("slope","slope",-0.3,-10.,10.);
    RooPolynomial linear("linear","linear",mass,RooArgSet(slope));
    
    RooRealVar frac("frac","frac",0.2,0.,1.);
    RooAddPdf model("model","model",RooArgList(gaus,linear),RooArgList(frac));

    RooRealVar ns("ns","# of signal",2000.,0.,20000.);
    RooRealVar nb("nb","# of background",8000.,0.,20000.);
    RooAddPdf model_ext("model_ext","model w/ ext likelihood",
                        RooArgList(gaus,linear),RooArgList(ns,nb));
    
    RooFitResult *res = model.fitTo(data,Save(true),Minos(true));
    RooAbsReal* nll = model.createNLL(data);
    
    TH1D *scan_std = new TH1D("scan_std","Standard Likelihood",100, 1850., 2200.);
    for(int bin=1; bin<=scan_std->GetNbinsX(); bin++) {
        frac.setVal(scan_std->GetBinCenter(bin)/10000.);
        frac.setConstant(true);
        model.fitTo(data);
        scan_std->SetBinContent(bin,(nll->getVal()-res->minNll())*2.);
    }
    
    RooFitResult *res_ext = model_ext.fitTo(data,Save(true),Minos(true));
    RooAbsReal* nll_ext = model_ext.createNLL(data);

    TH1D *scan_ext = new TH1D("scan_ext","Extended likelihood",100, 1850., 2200.);
    for(int bin=1; bin<=scan_ext->GetNbinsX(); bin++) {
        ns.setVal(scan_ext->GetBinCenter(bin));
        ns.setConstant(true);
        model_ext.fitTo(data);
        scan_ext->SetBinContent(bin,(nll_ext->getVal()-res_ext->minNll())*2.);
    }
    
    scan_std->SetStats(false);
    scan_std->SetLineWidth(2);
    scan_std->SetLineColor(kRed);
    scan_std->SetMinimum(-1.);
    scan_std->SetMaximum(12.);
    scan_std->GetXaxis()->SetTitle("frac");
    scan_std->Draw("axis");
        
    TLine lin;
    lin.SetLineColor(kGray+2);
    lin.SetLineStyle(kDashed);
    for(int n=0; n<=3; n++)
        lin.DrawLine(1850.,n*n,2200.,n*n);
    
    scan_std->Draw("csame");
    scan_ext->SetStats(false);
    scan_ext->SetLineWidth(2);
    scan_ext->SetLineColor(kRed);
    scan_ext->SetLineStyle(kDashed);
    scan_ext->Draw("csame");
}