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1 -------------------------------------------------------------------
2
3 =========================================================
4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
5 =========================================================
6
7 TestPolarization
8 ----------------
9
10 How to compute and plot the QED processes including
11 polarization.
12 Two possible scenarios are available:
13 - Polarization transfer of an incoming beam to final state particles
14 - Material dependent transmission of a polarized beams.
15 The method is explained below : see item Physics.
16
17 1- GEOMETRY DEFINITION
18
19 The geometry consists of a single block of a homogeneous material,
20 placed in a world.
21
22 Three parameters define the geometry :
23 - the material of the box,
24 - the thickness of the box (sizeZ),
25 - the transverse dimension of the box (sizeXY).
26
27 The default geometry (5mm of Iron, G4_Fe) is constructed in
28 DetectorConstruction, but the above parameters can be changed
29 interactively via the commands defined in DetectorMessenger.
30 Its polarization can be accessed via the PolarizationMessenger
31 (see example macro file), and is given in the global coordinate
32 system.
33
34 2- PHYSICS LIST
35
36 The Physics List contains QED particle definitions (electrons,
37 positrons and photons) and a general transportation process.
38 In addition the user can add one of the two process modules:
39 1. "standard" - standard (unpolarized) EM physics
40 2. "polarized" - polarized EM physics
41 These physics list contain the standard electromagnetic processes.
42
43 3- AN EVENT : THE PRIMARY GENERATOR
44
45 The primary kinematic consists of a single particle starting
46 at the edge of the box. The type of the particle and its
47 energy are set in PrimaryGeneratorAction (10 MeV electron).
48 By default the ParticleGun polarization is zero.
49 All parameter can be changed via the G4 build-in commands of
50 ParticleGun class (see the macros provided with this example).
51
52 4- PHYSICS
53
54 This example uses the following physics processes:
55
56 - electromagnetic:
57 photo-electric effect
58 Compton scattering
59 pair production
60 bremsstrahlung
61 ionization
62 multiple scattering
63 annihilation
64 or
65 - polarized electromagnetic:
66 (incl. simulation of polarization transfer, and
67 asymmetries for longitudinally polarized leptons, and
68 circularly polarized photons)
69
70 polarized photo-electric effect
71 polarized Compton scattering
72 polarized pair production
73 polarized bremsstrahlung
74 polarized ionization
75 multiple scattering
76 polarized annihilation
77 and
78 - transportation
79
80 and defines the following particles:
81 electron, positron, photon
82
83
84 5- HISTOGRAMS
85
86 The test contains 12 built-in 1D histograms, which are managed by the
87 HistoManager class and its Messenger. The histos can be individually
88 activated with the command :
89 /analysis/h1/set id nbBins valMin valMax unit
90 where unit is the desired unit for the histo (MeV or keV, etc..)
91 (see the macro histos.mac).
92
93 1 gamma energy
94 2 gamma cos(theta)
95 3 gamma phi
96 4 gamma polarization
97 5 electron energy
98 6 electron cos(theta)
99 7 electron phi
100 8 electron polarization
101 9 positron energy
102 10 positron cos(theta)
103 11 positron phi
104 12 positron polarization
105
106 6- VISUALIZATION
107
108 Simulated events can be displayed on top of a representation of
109 the geometry, see vis.mac for an example.
110
111 7- HOW TO START ?
112
113 compile and link to generate an executable
114 % gmake
115
116 execute Pol01 in 'batch' mode from the default macro file :
117 % Pol01 pol01.in
118
119 or execute Pol01 in 'batch' mode including analysis output :
120 % Pol01 histos.mac
121
122 if available use JAIDA to display the results via
123 % gmake plots
124
125 a visualisation example is available by calling
126 % Pol01
127 [...]
128 PreInit> /control/execute vis.mac
