class AtlTopPairFinder: public AtlKinFitterTool

 Top Pair Event Finder

 This Finder is looking for events with top pairs whereas one W-boson decays leptonically
 ( W -> e nu, w-> mu nu ) and one decays hadronically ( W -> jj ). Reconstruction of the
 W-bosons and top-quarks is carried out by employing a kinematic fit.

 First, the finder makes sure that sufficient numbers of physics objects for the
 reconstruction of a top pair are present in the event. This requires the following:

  - 4 jets
  - 1 lepton

 Since there is no requirement concerning b-jets some special cases have to be taken into
 account:

  - 0 b-jets in b-jet list:   b-jet list is replaced by jet list
  - 1 b-jet in b-jet list:    b-jet list is replaced by jet list, if statement makes sure that
                              the b-jet in the event is used for the b-jets of the candidates
  - > 2 b-jets in b-jet list: list is kept as it is

 Because of the case with 1 b-jet in the list the information concerning the tagger (type
 and cut weight) have to be given to the finder. This is not optimal and if someone has a
 solution it would be highly appreciated.

 Now the top pair candidates are built by combining the contents of the lists (jet list,
 b-jet list, lepton list). If-statements make sure that all candidates are unique. The evaluation
 of the candidates takes place and assigns a chi2 and a chi2 probability value to each candidate.
 All candidates that satisfy a certain chi2prob cut are recorded in the event and may be
 accessed at a later point in the analysis via fEvent->GetTopPairs().
 The candidate with the lowest chi2 (the highest chi2 probability) is deemed to be best top pair of
 the event. It is stored in the variable fBestTopPair and may be obtained from the TopFinder via
 the GetBestTopPair() - method.



 When the AtlTopCommonObjectsTool is used, all of the required information is provided automatically.
 In order to do this you have to give a pointer of the AtlTopCommonObjectsTool itself to the top #
 finder. How this is done is illustrated in the AtlFlavorRatioAnalysis in libTTbar.

 The fitter will use the first n jets from the fJets list provided by the user. The number of jets n can be set
 by the user with fJets_N_Max. The default is 20 jets. Take care that the fJets list is sorted when forwarding them to the fitter.


    Author: Felix Thomas <mailto:Felix.Thomas@mailbox.tu-dresden.de>
    Update: $Id: AtlTopPairFinder.cxx,v 1.26 2014/01/29 09:42:07 schlichte Exp $
    Copyright: 2010 (C) Felix Thomas