Hello,

I am trying to get the number (or fraction) of signal events vs background events in a range. I have tried a few different ways.

First off here is my code and plot:

```
#ifndef __CINT__
#include "RooGlobalFunc.h"
#endif
#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooDataHist.h"
#include "RooGaussian.h"
#include "TCanvas.h"
#include "RooPlot.h"
#include "TTree.h"
#include "TH1D.h"
#include "TRandom.h"
using namespace RooFit ;
void roofitmacro()
{
//Import histo from file
TFile f("analysis_hist.root","READ");
TH1D *kmass = new TH1D("kmass","kaon mass with fit",100 , 450, 600);
kmass = (TH1D*)f.Get("hkmass");
//create roofit variable
RooRealVar x("x","x",450,600) ;
//create roofit gaussian
RooRealVar mean("mean","mean",498,490,510) ;
RooRealVar sigma("sigma","sigma",9,7,11) ;
RooRealVar sig_yield("sig_yield","signal yield",1000000,0,3000000);
RooGaussian gauss("gauss","signal p.d.f.",x,mean,sigma) ;
//create roofit quadratic
RooRealVar c1("c1","coefficient of x term",400, 300, 600.) ;
RooRealVar c2("c2","coefficient of x^2 term",-0.4, -1, 0.1) ;
RooRealVar bkg_yield("bkg_yield","background yield",3000000,0,4000000);
RooPolynomial bkg("bkg","background", x, RooArgList(c1,c2)) ;
//create composite model model(x) = sig_yield*gauss(x) + bkg_yield*bkg(x)
RooAddPdf model("model","model",RooArgList(gauss,bkg),RooArgList(sig_yield,bkg_yield)) ;
//imposrt data from hist
RooDataHist data("data","dataset with K0 mass",x,kmass) ;
//fit model to data
model.fitTo(data,Extended(),Save());
//roofit's version of a canvas:
RooPlot* xframe = x.frame(Title("Kaon Mass with Gaussian Fit and Quadradic Background")) ;
//plot
data.plotOn(xframe) ;
model.paramOn(xframe, Layout(0.5, 0.9, 0.9) );
model.plotOn(xframe) ;
model.plotOn(xframe,Components(bkg),LineColor(kGreen));
xframe->Draw();
//create canvas to save it on
TCanvas *c = new TCanvas("c","c",1);
xframe->Draw();
c->Print("PLOTS/kmass_roofit.pdf");
}
```

I know I can do `sig_yield.getVal()`

and it will give me the total num of events (233141) but I want the number of events in a 2sigma range around the peak.

I have tried using `createIntegral(x)`

and `createIntegral(x,Range("signal"))`

:

```
cout << "nevents sig total = " << sig_yield.getVal() << endl;
double xmin = mean.getVal() - 2*sigma.getVal();
double xmax = mean.getVal() + 2*sigma.getVal();
x.setRange("signal",xmin,xmax);
RooAbsReal *Imodel = model.createIntegral(x);
cout << "Imodel = " << Imodel->getVal() << endl;
RooAbsReal *Imodel_sig = model.createIntegral(x,Range("signal"));
cout << "Imodel signal = " << Imodel_sig->getVal() << endl;
RooAbsReal *Ibkg = bkg.createIntegral(x);
cout << "Ibkg = " << Ibkg->getVal() << endl;
RooAbsReal *Ibkg_sig = bkg.createIntegral(x,Range("signal"));
cout << "Ibkg signal = " << Ibkg_sig->getVal() << endl;
RooAbsReal *Isig = gauss.createIntegral(x);
cout << "Isig = " << Isig->getVal() << endl;
RooAbsReal *Isig_sig = gauss.createIntegral(x,Range("signal"));
cout << "Isig signal = " << Isig_sig->getVal() << endl;
cout << "Ibkg + Isig = " << (Ibkg->getVal() + Isig->getVal() ) << endl;
cout << "Ibkg_sig + Isig_sig = " << (Ibkg_sig->getVal() + Isig_sig->getVal() ) << endl;
```

which outputs:

```
nevents sig total = 233141
[#1] INFO:Eval -- RooRealVar::setRange(x) new range named 'signal' created with bounds [480.094,514.946]
Imodel = 1.2572e+07
Imodel signal = 2.96325e+06
Ibkg = 1.44151e+07
Ibkg signal = 3.39767e+06
Isig = 21.8405
Isig signal = 20.8467
Ibkg + Isig = 1.44151e+07
Ibkg_sig + Isig_sig = 3.39769e+06
```

but these outputs do not make sense.

- Background should not be larger than the total
- Number of signal events is 233141 so integrating over gaussian signal should get me something close to that, not roughly 21. Maybe the ~21 number is a percentage? but if so why is the background integral not a percentage too?
- Background yield is about 1.5 X 10^6 so why is background integral 1.4 X 10^7, an order of magnitude higher?
- Why do I get more events if I add signal and background integrals than if I just integrate over the model? Shouldn’t I get roughly the same number?

So I do no know what I am misunderstanding or doing wrong.

Thanks in advance for your help.

Sarah