$Id: README,v 1.6 2008/09/26 19:47:51 maire Exp $
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     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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                            TestEm15
                            --------

	How to compute and plot the final state of Multiple Scattering 
	considered as an isolated process.
	The method is exposed below : see item Physics. 
	
 1- GEOMETRY DEFINITION
 
 	It is a single box representing a 'semi infinite' homogeneous medium.
 	Two parameters define the geometry :
 	- the material of the box,
	- the (full) size of the box.
 	
 	The default geometry (100 m of water) is constructed in 
	DetectorConstruction, but the above parameters can be changed 
	interactively via the commands defined in DetectorMessenger.
 	
 2- PHYSICS LIST
 
 	The physics list contains the standard electromagnetic processes.
	In order not to introduce 'articicial' constraints on the step size, 
	there is no limitation from the maximum energy lost per step.  
 	 
 3- AN EVENT : THE PRIMARY GENERATOR
 
 	The primary kinematic consists of a single particle starting at the edge
	of the box. The type of the particle and its energy are set in 
	PrimaryGeneratorAction (1 MeV electron), and can be changed via the G4 
 	build-in commands of ParticleGun class (see the macros provided with 
 	this example).
 	
 4- PHYSICS
 
        All discrete processes are inactivated (see provided macros),
	so that Multiple Scattering is 'forced' to determine the first step of 
	the primary particle. The step size and the final state are computed 
	and plotted. Then the event is immediately killed.
	
	The result is compared with the 'input' data, i.e. with the cross
	sections stored in the PhysicsTables and used by Geant4.
	
	The stepMax command provides an additionnal control of the step size of
        the multiple scattering.
 	

 5- HISTOGRAMS
         
	The test contains 9 built-in 1D histograms, which are managed by the
	HistoManager class and its Messenger. The histos can be individually 
	activated with the command :
	/testem/histo/setHisto id nbBins  valMin valMax unit 
	where unit is the desired unit for the histo (MeV or keV, etc..)
	(see the macros xxxx.mac).
 		
        1       Multiple Scattering. True step length
	2	Multiple Scattering. Geom step length
	3	Multiple Scattering. Ratio geomSl/trueSl
	4	Multiple Scattering. Lateral displacement: radius
	5	Multiple Scattering. Lateral displac: psi_space
	6	Multiple Scattering. Angular distrib: theta_plane
	7	Multiple Scattering. Phi-position angle
	8	Multiple Scattering. Phi-direction angle
	9	Multiple Scattering. Correlation: cos(phiPos-phiDir)
	
	See below the note on histogram tools.
	
 	One can control the name and the type of the histograms file with 
	the commands:
 	/testem/histo/setFileName  name  (default testem15)
   	/testem/histo/setFileType  name  (default root)
	
        It is also possible to print selected histograms on an ascii file:
        /testem/histo/printHisto id
        All selected histos will be written on a file name.ascii  
        (default testem15)
    	
	Note that, by default, histograms are disabled. To activate them, 
	uncomment the flag G4ANALYSIS_USE in GNUmakefile. 	
 	 				
 6- VISUALIZATION
 
 	The Visualization Manager is set in the main().
 	The initialisation of the drawing is done via the commands
 	/vis/... in the macro vis.mac. To get visualisation:
 	> /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.
	
 7- HOW TO START ?
 
	compile and link to generate an executable
 		% cd geant4/examples/extended/electromagnetic/TestEm15
 		% gmake
 		
	execute TestEm15 in 'batch' mode from macro files :
 		% TestEm15   compt.mac
 		
	execute TestEm15 in 'interactive mode' with visualization :
 		% TestEm15
		Idle> control/execute vis.mac
 		....
 		Idle> type your commands
 		....
 		Idle> exit
 

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