Spectrum fitting with RooFit --> errors

Dear all,

as usual, since I still don’t manage to get confident with RooFit, I am here to submit to experts my problem, with the hope that someone manages to help me in finding the solution.

In this case I have a histogram which is a dN/dpt spectrum.
First of all, I need to fit it with some PDFs which are suitable for my case (the Levy function, which I built by myself using the RooClassFactory since I didn’t find in the list of the available ones, and a simple exponential).
Since I know that PDFs are by default normalized, how can I then extract the integral of the PDF after the fit and its error?

Moreover, I need also to compute the with its error (computed by propagating those obtained from the fit). Is there a way to do this after having fitted the function?

Finally. Since I am used to the ‘old’ ROOT fit method, in order to have a more correct fit, I did a chi2 fit (not likelihood) with the options “EIM”, which in turn mean: best Error estimation, match the Integral of the function in the bin instead of its value at the center of the bin, and iMprove the fit (this should be an option in MINUIT). How can I set the fit in RooFit in order to do a chi2 fit and to set up the same behaviour determined by these options in the standard ROOT fit?

Thanks, best regards