$Id: README,v 1.17 2008/09/18 16:42:07 maire Exp $
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     =========================================================
     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
     =========================================================

                            TestEm6 
                            -------
     This example is intended to test the processes of gamma conversion
     to a pair of muons and annihilation of positrons with atomic
     electrons to a pair of muons.
     To make these process more visible, the usually much more frequent
     gamma conversion to a pair of electrons and the standard positron
     processes are not selected in the physics list.
	
 1- GEOMETRY DEFINITION
 
     The geometry consists of a single block of a homogenous material.
     	
     Two parameters define the geometry :
 	- the material of the box,
	- the (full) size of the box.
     The default is 500 m of iron.
     	 	
     In addition a transverse uniform magnetic field can be applied.
 	
     The default geometry is constructed in DetectorConstruction class,
     but all of the above parameters can be changed interactively via
     the commands defined in the DetectorMessenger class.
 	
 2- PHYSICS LIST
 
     The particle list is the one of novice/exampleN03.
     The physics list contains the 'standard' electromagnetic processes,
     and decay.
     
     For Gamma, only the GammaConversionToMuons has been registered.
     Futhermore, a high production cut (1 km, which gives infinity in energy)
     prevent any production of delta-electrons from ionization or gamma
     from bremsstrahlung.
     For Positrons, only the annihilation process is selected.
 		
 	 
 3- AN EVENT : THE PRIMARY GENERATOR
 
     The primary kinematic consists of a single particle which hits the
     block perpendicular to the input face. The type of the particle
     and its energy are set in the PrimaryGeneratorAction class, and can
     changed via the G4 build-in commands of ParticleGun class (see
     the macros provided with this example).
     The default is a Gamma of 100 TeV.
     	
     In addition one can choose randomly the impact point of the incident
     particle. The corresponding interactive command is built in
     PrimaryGeneratorMessenger class.
	 	
     A RUN is a set of events.
 	
 				
 4- 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 longitudinal view of the box.
 	
     The tracks are drawn at the end of event, and erased at the end of run.
     Optionaly one can choose to draw all particles, only the charged one,
     or none. This command is defined in EventActionMessenger class.

 5- PHYSICS DEMO

     The particle's type and the physic processes which will be available
     in this example are set in PhysicsList class.

     In addition a build-in interactive command (/process/inactivate proname)
     allows to activate/inactivate the processes one by one.

     The threshold for producing secondaries can be changed.
     eg: /run/particle/setCut 100 micrometer
         /run/initialize
	 
     To visualize the GammaConversionToMuons :
        /control/execute run01.mac
	/control/execute vis.mac
	/run/beamOn
		 
     To visualize the AnnihiToMuPair :
        /control/execute run11.mac
	/control/execute vis.mac
	/run/beamOn
		  	
 6- HOW TO START ?
 
     - compile and link to generate an executable
	% cd geant4/examples/extended/electromagnetic/TestEm6 
 	% gmake
 		
     - execute Test  in 'batch' mode from macro files
 	% TestEm6    run01.mac
 		
     - execute Test  in 'interactive mode' with visualization
 	% TestEm6 
 		....
 	Idle> type your commands
 		....
 	Idle> exit
 
 7- HOW TO INCREASE STATISTICS ON gamma -> mu+mu- ?
 
     The processes of gamma -> mu+mu-  and e+e- -> mu+mu-
     have a low cross section but can be important
     for leakage through thick absorbers and calorimeters.
     Straight forward simulation will be quite time consuming.
     To make the processes more visible, the cross section can be
     artificially increased by some factor (here 1000)
     using the commands  (only effective after  /run/initialize)

     /testem/phys/SetGammaToMuPairFac  1000
     /testem/phys/SetAnnihiToMuPairFac 1000
 
	
 8- HISTOGRAMS
 
  Testem6 produces 6 histograms which illustrate the final state of 
  the GammaConversionToMuons process. See their definitions in RunAction.cc   

  By default the histograms are not activated. To activate histograms
  the environment variable G4ANALYSIS_USE should be defined. For instance
  uncomment the flag G4ANALYSIS_USE in GNUmakefile.

  Before compilation of the example it is optimal to clean up old files:
	gmake histclean
	gmake
	
  By default the histograms are saved as testem6.root
  It is possible to choose the format of the histogram file (hbook, root, XML):
  comment/uncomment 1 line in the constructor of RunAction. 

  To use histograms, at least one of the AIDA implementations should be 
  available. See InstallAida.txt
