howto_classes

A few words on how to use Vuko's analysis classes
to run on the latino tree:

Basic goals:
- Be as much as possible independent of the latino
  tree flat structure and variable names, especially
  for things which are subject to frequent changes,
  like leptons, jets, ...

- Declare vector of more intelligent objects to 
  use in the analysis, e.g. LorentzVectors, that
  are easy to work with and to loop over

- Corrolary of the two first goals: "intelligent" objects
  are created from the flat latino tree variables in JUST ONE
  place: if the tree variable change, there's just one
  place that needs to be modified.

- Writing a new analysis should require as little 
  new code as possible and be able to built on basic
  stuff: event accepted? List of used leptons, ...


Basic design features:

- Defined new class "WZEvent" which inherits from the
  tree class created with MakeClass() in ROOT. That
  class among others contain:
  > vectors of reco and gen leptons, jets
  > has method telling you whether the event
    is passing selection and in which channel

- Defined simple reco and gen lepton classes,
  inherit from TLorentzVector and contain the 
  basic info you want to know about a vector.
  The WZEvent has vectors of these objects.

TODO: 
 > the reco lepton class should implement scale factors per
   lepton, as these depend only on the lepton id and kinematics
 > WZEvent should tell you which of these leptons were used
   for the WZ final state

- To do an analysis on selected (or all events)
  and build on all of the above, I am defining
  a WZAnalysis class, look at the example which
  currently does the a gen analysis to check
  that BRs are correctly implemented in the WZ MC.
  A similar class is used for the Unfolding analysis.


Random instructions

- If you change the base tree class because 
  more variables are added, names are changed, etc.
  You need to change:
   > Define the new class name at the top of WZEvent.h
   > If needed modify the implementation of the ReadEvent()
     method in WZEvent.C
   > Define the new class name in wzToolsNew.C