Hey,

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?

Thanks!

Hey,

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?

Thanks!

I canâ€™t make these options work. What are the conditions on the parameters\variables the functions take?

Thanks!

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 donâ€™t get a good fit with the Bukin and when I convolute the Novosibirsk with Breit-Wigner, I get weird discontinuities in the fitâ€™s derivative, which doesnâ€™t make too much sense if the function is like the one in the link.

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Itâ€™s hard to say whatâ€™s going on. Could you post a PDF of the fit thatâ€™s not working?

For the convolution:

Itâ€™s probably a numerical convolution using FFTs. FFTs can be a bit tricky if you donâ€™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.