I’m actually just trying to scale the pT of the tracks in the range 0<pT<30GeV by the given Fermi-like function above, while leaving pT>30GeV tracks in the RooDataSet untouched. I’m doing this by creating two subsets of the original RooDataSet (one for each pT range), and then applying a scale factor (the Fermi function) to the lower pT dataset. I then combine the two datasets and perform an unbinned ML fit. But like I said above, it doesn’t seem the lower pT dataset is being scaled like I want. Does anyone know a simpler way to do this?