{
    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));
    
    RooFitResult *res = model.fitTo(data,Save(true),Minos(true));
    RooAbsReal* nll = model.createNLL(data);
    
    TH1D *nll_scan = new TH1D("nll_scan","Likelihood scan",200, 0.185, 0.22);
    for(int bin=1; bin<=nll_scan->GetNbinsX(); bin++) {
        frac.setVal(nll_scan->GetBinCenter(bin));
        nll_scan->SetBinContent(bin,(nll->getVal()-res->minNll())*2.);
    }
    
    nll_scan->SetStats(false);
    nll_scan->SetLineWidth(2);
    nll_scan->SetMinimum(-1.);
    nll_scan->SetMaximum(12.);
    nll_scan->GetXaxis()->SetTitle("frac");
    nll_scan->Draw("axis");
    
    TBox box;
    box.SetFillColor(kRed-10);
    RooRealVar* best_frac = (RooRealVar*)res->floatParsFinal().find("frac");
    box.DrawBox(best_frac->getVal()+best_frac->getErrorLo(),-0.5,
                best_frac->getVal()+best_frac->getErrorHi(),+12.);
    
    TLine lin;
    lin.SetLineColor(kGray+2);
    lin.SetLineStyle(kDashed);
    for(int n=0; n<=3; n++)
        lin.DrawLine(0.185,n*n,0.22,n*n);
    
    nll_scan->Draw("csame");
}