Having events at 0 while plotting RooPlot

Dear Experts,

I am importing histogram from root file and while plotting the histogram, I am having these additional events at 0, as shown in the following figure which shouldn’t be here.
1

Original histogram in root file is like this i.e. it contains only 32 events. None of the event occurs at zero.
z

Could anyone tell me why is this happening? Piece of code i’m using is:

a

But for the histograms having large number of events, the same code is working fine.

Thank you in advance!

Can you provide the root file ?

Here it is:
gamma.root (3.8 KB)

“energy” is the histogram i’m interested in.

Thank you!

It seems RootPlot uses the option E0:

 energy->Draw("E0")

… gives the same. Can you set the drawing option used by RooPlot ?

Hi,

I guess i can change drawing options by:

dh.plotOn(plot,Name(“hh”),DrawOption(“P”));
plot->Draw();

I tried different drawing options, it changes the styles but additional events at still there.

I found this post. I think alot of people were having the same problem but there isn’t available a good solution for it.

What about : DrawOption(“E”) ?
May be @moneta has an idea ?

Indeed option E0 gives:


Which is a bit different from what you get as there is no error bars won the Point at ). So RooPlot seems to do something else. @moneta ta is the expert in that area.

With Option “E” it still plots error bars for events at 0.

1

Yes, so it is something else, not related to graphics.

RooPlot by default plots the Poisson error. You can have this behaviour for an histogram, by calling
TH1::SetBinErrorOption(TH1::kPoisson).
This will give you an error bar for bins with zero entries.
There will be a remaining difference. For ROOT the error at bin 0 is ~ 1.8, while in RooFit is ~ 1.2. This is because RooFit uses for that case the 1-side 68% interval while ROOT the 2-side interval. It is a question of definition, but my preference is for keeping the same procedure (2-side intervals) independent of the number of observed events.

Lorenzo

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