Hi all,
I am trying to use RooFit to fit a mass peak shape with the following features:
- Mass peak defined by a CBShape.
- Peaking background 1, CBShape.
- Peaking background 2, CBShape.
- Non peaking background, RooExponential.
And I need to extract, essentially, the yield of the mass peak. My problem is the following: I want to restrict the yield of the peaking backgrounds to a certain fraction of the yield of the data:
N_bkg,i = N_peak*f
But letting f vary. If I only had one peaking background, I would do something like
NexpExpPDF+Npeaking(f*CB_bkg1+(1-f)*CB_peak)
and I would extract de yield from Npeaking*(1-f). However, if I add a second peaking background
NexpExpPDF+Npeaking(f1CB_bkg1+f2CB_bkg2+(1-f1-f2)*CB_peak)
now the f1 and f2 don’t have the meaning I want --that is, a fraction of the CB_peak yield.
I have not been able to find a workaround for this, but I’m sure somebody has found a similar problem at some point. Any ideas would be very much appreciated!
Thanks,
Albert
PD: On another note, I don’t like very much the logical composition of the model, because one would like to have the background on one side (with dependences on N_peak). However, if I used a RooFormulaVar to modelize N_bkg1 the possible variations of f1 are lost…