Double Sided Crystal Ball - does it exist in RooFit?


I wish to fit a sugnal with 2-sided crystal ball function. My question is whether such a thing already exists in RooFit (and if it does, how should I implement it?) or should I just sum it with an exponential for the other tail?


Maybe what you search is a Bukin PDF or the RooNovosibirsk function?

I can’t make these options work. What are the conditions on the parameters\variables the functions take?


For the Bukin constructor we e.g. have (this documentation will soon show up on the root master docs):

Construct a Bukin PDF.
\param name  The name of the PDF for RooFit's bookeeping.
\param title The title for e.g. plotting it.
\param _x    The variable.
\param _Xp   The peak position.
\param _sigp The peak width as FWHM divided by 2*sqrt(2*log(2))=2.35
\param _xi   Peak asymmetry. Use values around 0.
\param _rho1 Left tail. Use slightly negative starting values.
\param _rho2 Right tail. Use slightly positive starting values.
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I don’t get a good fit with the Bukin and when I convolute the Novosibirsk with Breit-Wigner, I get weird discontinuities in the fit’s derivative, which doesn’t make too much sense if the function is like the one in the link.

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It’s hard to say what’s going on. Could you post a PDF of the fit that’s not working?

For the convolution:
It’s probably a numerical convolution using FFTs. FFTs can be a bit tricky if you don’t use enough bins. If you want to pursue this further, I can look for a post where we discussed this in a bit more detail.