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fitting.md
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fitting.md
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# Fitting procedures
## Fitting meson resonances
Best overview of types of fits and theoretical motivations for each of those can be
found in section
["Resonances" of the _PDG_](http://pdg.lbl.gov/2018/reviews/rpp2018-rev-resonances.pdf).
- BESIII is a _formation experiment_.
See documentation for all `RooFit` parametrizations
[here](https://root.cern/doc/master/group__Roofit.html).
### Single and double Gaussian
Characterization of detector resolution(s).
### Breit-Wigner parametrization
- Only works in case of _narrow structure_ and if there are no other resonances nearby
- Can be used to extract _pole parameters_ such as particle width
- Possible: energy dependent parameters
- Convolution of a Breit-Wigner with a Gaussian is called a _Voigtian_ (see
[RooVoigtian](https://root.cern.ch/doc/master/classRooVoigtian.html)).
### Flatté parametrization
- Analytical continuation of the Breit-Wigner parametrization
- Does not allow for extraction of pole parameters, only ratios
## Background shapes
- [Polynomial](https://root.cern/doc/master/classRooPolynomial.html)
- [Chebychev polynomial](https://root.cern.ch/doc/master/classRooChebychev.html)
- [Argus background shape](https://root.cern/doc/master/classRooArgusBG.html)
## Other literature
- [LHCb GitBook on RooFit](https://lhcb.github.io/ostap-tutorials/fitting/decorations.html)
- [Example scripts for RooFit](https://root.cern.ch/root/html/tutorials/roofit/index.html)
(see overview of descriptions
[here](https://root.cern.ch/doc/master/group__tutorial__roofit.html))