
     =========================================================
     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
     =========================================================

                             lArCal 
                            --------

 This example is intended to simulate the Forward Liquid Argon Calorimeter
 (FCAL) of the ATLAS Detector at LHC. The goal of the FCAL is to provide
 a good missing energy determination in the region of very small angles 
 from the beam direction. 


 1. GEOMETRY DEFINITION
 ------------------------

 The liquid Argon calorimeter consists of three modules with the same
 nominal outer dimensions: an electromagnetic module (made
 of copper) followed by two hadronic ones (made of tungsten alloy). 
 The corresponding parameters of these modules are defined inside the
 FCALEMModuleParameters.input and FCALHadModuleParameters.input files.
 The package contains as well a FCALTestbemSetup class whose geometry is given by 
 FCALTestbeamSetupParameters.input. See these files for details concerning to
 radius, lenght and angles of the different components. 


 2.  AN EVENT : THE PRIMARY GENERATOR
 ------------------------------------ 
    
 The primary kinematic consists of a single particle which hits the
 geometry perpendicular to the input face. The FCALPrimaryGeneratorAction 
 class gives the particle and its energy (by default it is an electron of
 20 GeV). These parameters can be changed in commands of ParticleGun class
 inside the macros given in this example. 
 
 The subdirectory data-tracks contains the kinematic files 
 of the particles for different energies (20 GeV, 40 GeV, 60 GeV, 80 GeV, 
 120 GeV and 200 GeV). 
 The information given inside these files are the X, Y, Z and cosX, 
 cosY, cosZ variables for each event. 

  A RUN is a set of events.
 	

 3. VISUALIZATION
 ------------------

 The Visualization Manager is set in the main().
 The initialisation of the drawing is done via the command
 > /control/execute vis.mac
 	
 The detector has a default view which is a transversal view of the geometry.

 The tracks are drawn at the end of event, and erased at the end of run.
 Optionally the way of drawing the particles can be changed in the
 TBEVentActionMessenger class.  


 4. PHYSICS
 ----------

 You can select between 4 Physics Lists: QGSP, LHEP, QGSC, QGSP_BIC_EMY.
 The last one is set as default, so that you can test the low-energy 
 electromagnetic.
 The selection is done simply by comment/uncomment a line in the main
 lArCal.cc  (look for the keyword  ***LOOKHERE***).


 5. HOW TO START ?
 ----------------- 

 - compile and link to generate an executable
      % cd geant4/examples/advanced/lAr_calorimeter
      % gmake
 		
 - execute the program  in 'batch' mode from macro files
      % lArCal prerunlArcal.mac
 		
 - execute Test  in 'interactive mode' with visualization
      %  lArCal 
         ...
      Idle> type your commands
         ...
      Idle> exit


 6. HISTOGRAMS
 --------------
 The analysis is performed using the histogramming tools provided by 
 Geant4. No external dependencies are required.
 
 lArCal produces 4 histograms (saved as fcal.root) which illustrate
 the final state of the most important variables of the example:

 Histo1 --> Number of tracks out of World
 Histo2 --> Number of secondary particles
 Histo3 --> Total energy deposited (in MeV) in the electromagnetic module
 Histo4 --> Total energy deposited (in MeV) in the hadronic module

 See their definitions in FCALRunAction.cc 

 The histograms are saved (default) as a ROOT file. It is possible to save the 
 histograms in a xml file by editing 
   include/FCALAnalysisManager.hh
 (comment g4root.hh and uncomment g4xml.hh)

 
