Gfitter - A Generic Fitter Project for HEP Model Testing

The generic fitting package Gfitter comprises a framework for the statistical analysis of parameter estimation problems in HEP. It is specifically designed to provide a user-friendly environment for involved fitting problems, such as the global Standard Model fit to electroweak precision data. During its development, it was found that Gfitter is also a convenient framework for averaging problems, ranging from simple weighted means using or not correlated input data, to more involved problems with common systematic errors, requiring or not parameter rescaling.

The software package consists of abstract object-oriented code in C++ using ROOT functionality. Tools for the handling of the data, the fitting, and statistical analyses such as toy Monte Carlo sampling are provided by a core package, where theoretical errors, correlations, and inter-parameter dependencies are consistently dealt with. Theoretical models are inserted as plugin packages, which may be hierarchically organised. The use of dynamic parameter caching avoids the recalculation of unchanged results between fit steps, and thus significantly reduces the amount of computing time required for a fit.

The Gfitter package can be used for an interpretation of experimental data in different theoretical frameworks. We have performed analyses in the framework of the electroweak Standard Model (SM), a Two-Higgs-Doublet-Model, and various other extensions of the SM, like a fourth fourth fermion generation, two Higgs doublet, inert Higgs and littlest Higgs models, models with large, universal or warped extra dimensions and technicolour.

The development of the software and the physics studies with Gfitter are done in very close collaboration with scientists from CERN and DESY. More details can be found at the homepage of the Gfitter project.