$Id: README,v 1.4 2002/06/05 14:20:59 maire Exp $
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     =========================================================
     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
     =========================================================

                            TestEm6 
                            -------
     This example is intended to test the process of
     gamma conversion to a pair of muons.
     To make this process more visible, the usually much more frequent
     gamma conversion to a pair of electrons is 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.
 		
 	 
 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
	  	
 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- HISTOGRAMS
 
     Testem6 produces 6 histograms (saved as testem6.paw) which illustrate
     the final state of the GammaConversionToMuons process.
     See their definitions in RunAction.cc
     
     Note that histograms are disabled via the flag G4NOHIST in GNUmakefile.

 8- Using the Anaphe implementation of the AIDA 2.2 histograms:
    -----------------------------------------------------------

     In order to use the Anaphe implementation of the AIDA 2.2 interfaces, 
     prepare some environment variables by source-ing one of the following 
     startup scripts (depending on your compiler version):

     # gcc-2.95.2
     source $LHCXXTOP/share/LHCXX/4.0.1/install/sharedstart.sh or .csh

     # egcs_1.1.2 (aka gcc 2.91.66)
     source $LHCXXTOP/share/LHCXX/4.0.1-sec/install/sharedstart.sh or .csh

     At CERN, $LHCXXTOP is /afs/cern.ch/sw/lhcxx, you may want to use a
     more recent release, check http:/cern.ch/anaphe for more information.

     After this, you will have access to the 'aida-config' command which
     is used in the GNUmakefile.

 9- HOW TO INCREASE STATISTICS ON gamma -> mu+mu- ?
 
     The process of gamma -> mu+mu- has 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 process more visible, the cross section can be artificially
     increased by some factor (here 1000) using the command
     (only effective after  /run/initialize)

     /run/process/setGammaToMuPairFac 1000
 
