Hi Rooters,

I am using TFractionFitter in my analysis to have an estimate of the number of true photons entering into my sample.

Here are my inputs :

*** the data distribution

*** the true photon template

*** the fake photon template

All template distributions are based on photon shower shape variables.

The fitter allows me to have an estimate of number of true photons in my data distribution below some threshold value. But here is the trick. This threshold value depends on the photon pt which is not an info present in the template distributions.

I had the idea of making the fit with 2D histograms (shower shape vs its cut value) but I was wondering how to make the fitter understand that I want the fit to be performed only on shower shape info.

Also, my other question is how many entries roughly does one need in each template distribution ??? Is 100 sufficient ???

Then, my last question is the following. I would like to apply some parameters to my true template distribution before it enters the fit. I would like basically to do a+b*x where x is my template variable and then make it enter into the fit. But most important, I would like a and b to be left as parameters in the fit returning me the best values for agreement between data and MC. How can I do that ???

Thanks a lot for the help.