# Shape interpolation using two pdfs

Dear experts,

I have two signal mass points m1 and m2 and corresponding two pdfs which I get after fitting the mass observables Mgg and Mjj. Mgg fit is with Gaussian function and Mjj fit is with double-sided crystal ball function. I am sharing my workspace for m1=300 GeV and m2 = 400 GeV signal points at  (signal label = NMSSMX300ToY90H125 and NMSSMX400ToY90H125).

Since I do not have intermediate-mass simulation points (let’s say 350 GeV) between m1 and m2, I want to use an interpolation method using which I can get Mgg and Mjj pdfs for the 350 GeV signal point.

Could you please let me know if there is any straightforward way of doing this using roofit.

Thanks,

Lata

Hi @lata ,
we need @moneta or @jonas 's help here, let’s ping them.

Cheers,
Enrico

Hi,
It looks to me that your pdf’s are expressed in a functional form and not in term of an histogram. In this case you can maybe just interpolate the pdf parameters, that, if I have understood well you extract from a fit to the simulated data.
If this is not good enough you can try using a morphing algorithm available in RooFit and described by this example: ROOT: tutorials/roofit/rf705_linearmorph.C File Reference

Lorenzo

Hello @moneta ! Thanks for sharing Roofit function. It seems to work fine. I have only one query in the example code you shared. Let say if I pick alpha=0.5 that means it will be interpolated to the mid-mass point of two given mass m1 and m2. (e.g. m1= 300 GeV and m2=400 GeV so with alpha=0.5 it will interpolated for m=350 GeV)

And depending upon the binning of the alpha parameter, the projection will be made for other intermediate-mass points (let say binning I set 10 for alpha range [0,1], then alpha=0.2 will correspond to intermediate-mass point 320 GeV)

Best,
Lata

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