$Id: README,v 1.2 2007/12/04 10:34:17 schaelic Exp $
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     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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                            TestPolarization
                            ----------------

	How to compute and plot the QED processes including
	polarization.
	Two possible scenarios are available:
	- Polarization transfer of an incoming beam to final state particles 
	- Material dependent transmission of a polarized beams.
	The method is explained below : see item Physics. 
	
 1- GEOMETRY DEFINITION
 
	The geometry consists of a single block of a homogeneous material,
	placed in a world.
     	
	Three parameters define the geometry :
	- the material of the box,
	- the thickness of the box (sizeZ),
	- the  transverse dimension of the box (sizeXY).
	
        The default geometry (5mm of Iron, G4_Fe) is constructed in 
	DetectorConstruction, but the above parameters can be changed 
	interactively via the commands defined in DetectorMessenger.
        Its polarization can be accessed via the PolarizationMessenger
        (see example macro file), and is given in the global coordinate 
        system. 
 	
 2- PHYSICS LIST
 
	The Physics List contains QED particle definitions (electrons,
        positrons and photons) and a general transportation process.
        In addition the user can add one of the two process modules:
	 1. "standard"  - standard (unpolarized) EM physics
	 2. "polarized" - polarized EM physics 
 	These physics list contain the standard electromagnetic processes.
 	 
 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 (10 MeV electron).
        By default the ParticleGun polarization is zero.
        All parameter can be changed via the G4 build-in commands of
        ParticleGun class (see the macros provided with this example). 
 	
 4- PHYSICS
 
     This example uses the following physics processes:

       - electromagnetic:
           photo-electric effect
           Compton scattering
           pair production
           bremsstrahlung
           ionization
           multiple scattering
           annihilation
       or
       - polarized electromagnetic:
         (incl. simulation of polarization transfer, and
          asymmetries for longitudinally polarized leptons, and
          circularly polarized photons) 

           polarized photo-electric effect
           polarized Compton scattering
           polarized pair production
           polarized bremsstrahlung
           polarized ionization
           multiple scattering
           polarized annihilation
       and
       - transportation

     and defines the following particles:
        electron, positron, photon 


 5- HISTOGRAMS
         
	The test contains 12 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 macro histos.mac).

            1  gamma energy
            2  gamma cos(theta)
            3  gamma phi
            4  gamma polarization
            5  electron energy
            6  electron cos(theta)
            7  electron phi
            8  electron polarization
            9  positron energy
           10 positron cos(theta)
           11 positron phi
           12 positron polarization

        If AIDA is available, i.e. if G4ANALYSIS_USE is set, these
        histograms are stored in a compressed XML file
        (pol01.aida). These results can be displayed using a small
        program (plotResults.java) based on JAIDA by simply calling 

          % gmake plots
 	 				
 6- VISUALIZATION
 
     Simulated events can be displayed on top of a representation of 
     the geometry, see vis.mac for an example.
	
 7- HOW TO START ?
 
	compile and link to generate an executable
 		% gmake
 		
	execute pol01 in 'batch' mode from the default macro file :
 		% pol01   pol01.in

	or execute pol01 in 'batch' mode including aida output :
 		% pol01   histos.mac

        if available use JAIDA to display the results via
                % gmake plots

	a visualisation example is available by calling 
 		% pol01  
                [...]
                PreInit> /control/execute vis.mac