Dear roofit experts,
I want to check the robustness of a simultaneous fit of 6 independent data samples by using the pull method.
I use the RooMCStudy class to generate N new samples from the six original ones:
[color=#4040FF]RooMCStudy mcStudy(myPDF,myPDF,x,"","");
mcStudy.generate(nSamples,nEvents,kTRUE);
RooDataSet newData = (RooDataSet) mcStudy.genData(i);[/color] x6
(Since I use a simultaneous fit, I cannot use the generateAndFit function from RooMCStudy).
Then, I fit these new samples with the same PDF and store the final parameters values.
The resulting pull distributions are good (mu = 0 & sig = 1) for most of the variables except all the variables related to Signal amplitude (I don’t fit the direct signal amplitude, but combination variables as asymmetries and yield ratio) for which I found a width which is around 0.7.
I try to fit the direct signal amplitudes instead of combination one, or only fit 4 indepedendent samples. I obtain the same results.
Anyone have any idea of the origin of this 1/sqrt(2) factor ?
Thanks!
Léo.