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0002
0003 =========================================================
0004 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
0005 =========================================================
0006
0007 TestPolarization
0008 ----------------
0009
0010 How to compute and plot the QED processes including
0011 polarization.
0012 Two possible scenarios are available:
0013 - Polarization transfer of an incoming beam to final state particles
0014 - Material dependent transmission of a polarized beams.
0015 The method is explained below : see item Physics.
0016
0017 1- GEOMETRY DEFINITION
0018
0019 The geometry consists of a single block of a homogeneous material,
0020 placed in a world.
0021
0022 Three parameters define the geometry :
0023 - the material of the box,
0024 - the thickness of the box (sizeZ),
0025 - the transverse dimension of the box (sizeXY).
0026
0027 The default geometry (5mm of Iron, G4_Fe) is constructed in
0028 DetectorConstruction, but the above parameters can be changed
0029 interactively via the commands defined in DetectorMessenger.
0030 Its polarization can be accessed via the PolarizationMessenger
0031 (see example macro file), and is given in the global coordinate
0032 system.
0033
0034 2- PHYSICS LIST
0035
0036 The Physics List contains QED particle definitions (electrons,
0037 positrons and photons) and a general transportation process.
0038 In addition the user can add one of the two process modules:
0039 1. "standard" - standard (unpolarized) EM physics
0040 2. "polarized" - polarized EM physics
0041 These physics list contain the standard electromagnetic processes.
0042
0043 3- AN EVENT : THE PRIMARY GENERATOR
0044
0045 The primary kinematic consists of a single particle starting
0046 at the edge of the box. The type of the particle and its
0047 energy are set in PrimaryGeneratorAction (10 MeV electron).
0048 By default the ParticleGun polarization is zero.
0049 All parameter can be changed via the G4 build-in commands of
0050 ParticleGun class (see the macros provided with this example).
0051
0052 4- PHYSICS
0053
0054 This example uses the following physics processes:
0055
0056 - electromagnetic:
0057 photo-electric effect
0058 Compton scattering
0059 pair production
0060 bremsstrahlung
0061 ionization
0062 multiple scattering
0063 annihilation
0064 or
0065 - polarized electromagnetic:
0066 (incl. simulation of polarization transfer, and
0067 asymmetries for longitudinally polarized leptons, and
0068 circularly polarized photons)
0069
0070 polarized photo-electric effect
0071 polarized Compton scattering
0072 polarized pair production
0073 polarized bremsstrahlung
0074 polarized ionization
0075 multiple scattering
0076 polarized annihilation
0077 and
0078 - transportation
0079
0080 and defines the following particles:
0081 electron, positron, photon
0082
0083
0084 5- HISTOGRAMS
0085
0086 The test contains 12 built-in 1D histograms, which are managed by the
0087 HistoManager class and its Messenger. The histos can be individually
0088 activated with the command :
0089 /analysis/h1/set id nbBins valMin valMax unit
0090 where unit is the desired unit for the histo (MeV or keV, etc..)
0091 (see the macro histos.mac).
0092
0093 1 gamma energy
0094 2 gamma cos(theta)
0095 3 gamma phi
0096 4 gamma polarization
0097 5 electron energy
0098 6 electron cos(theta)
0099 7 electron phi
0100 8 electron polarization
0101 9 positron energy
0102 10 positron cos(theta)
0103 11 positron phi
0104 12 positron polarization
0105
0106 6- VISUALIZATION
0107
0108 Simulated events can be displayed on top of a representation of
0109 the geometry, see vis.mac for an example.
0110
0111 7- HOW TO START ?
0112
0113 compile and link to generate an executable
0114 % gmake
0115
0116 execute Pol01 in 'batch' mode from the default macro file :
0117 % Pol01 pol01.in
0118
0119 or execute Pol01 in 'batch' mode including analysis output :
0120 % Pol01 histos.mac
0121
0122 if available use JAIDA to display the results via
0123 % gmake plots
0124
0125 a visualisation example is available by calling
0126 % Pol01
0127 [...]
0128 PreInit> /control/execute vis.mac
