How to fit histograms with error bars set by user in RooFit?

[meng_wang]

Hi, guys.
I’m fitting a histogram with error bars in RooFit.
First, I set bin contents an bin errors for TH1F* h1;
Then
RooAbsData* data=new RooAbsData(“data”,“data”, x, h1);
model.fitTo(*data);
It seems that whether I set bin errors or not, the fit results are the same.

[moneta]

Hi,

If you are setting yourself bini errors, you must use the option, when fitting, RooFit::SumW2Error(true).
It would probably also make more sense to use the chi2 fit instead of the default likelihood, by using
model.chi2FitTo(…) instead of model.fitTo(…)

Lorenzo

[meng_wang]

Thanks for your help!
It works for me.
When I use model.chi2FitTo(), the errors of fit results are very large even if the fit status is OK.
Maybe I need to tune my parameters.

[moneta]

Hi,

The errors should be correct. If you are using RooFit::SumW2Error(true) and your data statistics is not too small, the error from the chi2 method or the likelihood one should be similar

Lorenzo

[meng_wang]

Thanks for your patience!