# P.d.f normalization integral is zero or negative

Hi,
I’m trying to plot a profile likelihood interval using:
ProfileLikelihoodCalculator pl(*data,mc);
pl.SetConfidenceLevel(0.95);
LikelihoodInterval
interval = pl.GetInterval();
LikelihoodIntervalPlot plot(interval);
plot.SetNPoints(50);
plot.Draw("");

When I do, I get a series of errors like this:
[#0] WARNING:Minization – RooMinimizerFcn: Minimized function has error status.
Returning maximum FCN so far (26831.6) to force MIGRAD to back out of this region. Error log follows
Parameter values: f=0.418067, mGau=0.665142, mLan=178.942, mu=0.3775, wG=1.53094, wL=34.3664
RooGaussian::SignalG[ x=Mjj mean=mGau sigma=wG ]
p.d.f normalization integral is zero or negative @ x=Mjj=44.3092, mean=mGau=0.665142 +/- 0.945268, sigma=wG=1.53094 +/- 1.15983
And so on…

Which I don’t understand. The PDF (a gaussian plus two landaus) is well behaved and the fit to data looks good. I guess I’m missing something.

Any suggestions would be welcome.

From the log I see you are having a Gaussian with x=44 and mu=0.66 and sigma=1.53. Are you sure the range of the Gaussian is not off the peak ?
This could explain the problem

Lorenzo

Thanks for the quick response. The Gaussian is set up with a mean of 38.32:
RooRealVar mGau(“mGau”,“Mean of Gaussian”,38.32,0,100) ;

And the signal+background fit looks just fine (should by definition since the toy MC data is generated with the same model)

I think it’s LikelihoodIntervalPlot that’s scanning over different values of mGau etc.

Yes it is correct that the LikelihoodINtervalPlot is scanning several parameter values. Which one is your parameter of interest (POI) ?
You can also set the POI range using LikelihoodIntervalPlot::SetRange(x1,x2)

Lorenzo

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