
---- Modify Mean_v4 and produce histograms of invariant mass ----

Include histograms inside "ParticleMass" class.

***
In "ParticleMass.h":
- define a "Particle" struct to hold
  - a string to be used as name,
  - a pointer to "MassMean",
  - a pointer to "TH1F",
- modify the STL array to hold pointers to "Particle" objects,
- declare a function "pCreate" to create a "decay mode" (use "bCreate"
  function in "ElementReco" as example).

***
In "MassMean.h,cc"
- change the "add" function to "bool" and return true or false for events
  in the mass range or not.

***
In "ParticleMass.cc":
- implement the function "pCreate" taking 3 arguments, one string and min-max
  masses; use the name as name for "TH1F" and min-max masses 
  to create the "MassMean" object; store the pointers of the objects;
- in "beginJob" replace the direct creation of "MassMean" object with 
  calls to "pCreate" for the 2 decay modes (use 0.495-0.500 and
  1.115-1.116 as ranges);
- in "endJob" loop over the Particle objects and for each one 
  get the event number, mean and rms masses and printout them, then
  save the histogram to file;
- in "process" loop over the ParticleMass objects, call the 
  "add" function for each "MassMean" object and fill the histogram
  with the invariant mass for the accepted events.
  Do not worry about multiple calls to "mass" function for the same event.

********* final list of functions *********

main                   copy   Mean_v4
mass                   copy   Mean_v4

********* final list of classes   *********

                       .h                            .cc
Event                  copy   Mean_v4                copy   Mean_v4
EventReadFromFile      copy   Mean_v4                copy   Mean_v4
EventSim               copy   Mean_v4                copy   Mean_v4
AnalysisSteering       copy   Mean_v4                copy   Mean_v4
EventSource            copy   Mean_v4                copy   Mean_v4
MassMean               modify Mean_v4                modify Mean_v4
ParticleMass           modify Mean_v4                modify Mean_v4
EventDump              copy   Mean_v4                copy   Mean_v4
Constants              copy   Mean_v4                copy   Mean_v4
Utilities              copy   Mean_v4                copy   Mean_v4
