Roofit without Normalization?

Hi,

I’m trying to fit a mass spectrum. And am having difficulty with using RooGenericPdf. It seems RooFit just draw a straight line no matter how I change the limits and seed value. Is it because of the normalization ? How do we switch it off temporarily ? The histogram goes flat as we go to higher masses, so the Generic Pdf I used was an exponential like an RC circuit…

Thanks alot.