1 | $Id: README,v 1.2 2007/12/04 10:34:17 schaelic Exp $ |
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2 | ------------------------------------------------------------------- |
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3 | |
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4 | ========================================================= |
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5 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP |
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6 | ========================================================= |
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7 | |
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8 | TestPolarization |
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9 | ---------------- |
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10 | |
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11 | How to compute and plot the QED processes including |
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12 | polarization. |
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13 | Two possible scenarios are available: |
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14 | - Polarization transfer of an incoming beam to final state particles |
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15 | - Material dependent transmission of a polarized beams. |
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16 | The method is explained below : see item Physics. |
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17 | |
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18 | 1- GEOMETRY DEFINITION |
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19 | |
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20 | The geometry consists of a single block of a homogeneous material, |
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21 | placed in a world. |
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22 | |
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23 | Three parameters define the geometry : |
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24 | - the material of the box, |
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25 | - the thickness of the box (sizeZ), |
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26 | - the transverse dimension of the box (sizeXY). |
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27 | |
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28 | The default geometry (5mm of Iron, G4_Fe) is constructed in |
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29 | DetectorConstruction, but the above parameters can be changed |
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30 | interactively via the commands defined in DetectorMessenger. |
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31 | Its polarization can be accessed via the PolarizationMessenger |
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32 | (see example macro file), and is given in the global coordinate |
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33 | system. |
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34 | |
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35 | 2- PHYSICS LIST |
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36 | |
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37 | The Physics List contains QED particle definitions (electrons, |
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38 | positrons and photons) and a general transportation process. |
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39 | In addition the user can add one of the two process modules: |
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40 | 1. "standard" - standard (unpolarized) EM physics |
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41 | 2. "polarized" - polarized EM physics |
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42 | These physics list contain the standard electromagnetic processes. |
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43 | |
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44 | 3- AN EVENT : THE PRIMARY GENERATOR |
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45 | |
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46 | The primary kinematic consists of a single particle starting |
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47 | at the edge of the box. The type of the particle and its |
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48 | energy are set in PrimaryGeneratorAction (10 MeV electron). |
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49 | By default the ParticleGun polarization is zero. |
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50 | All parameter can be changed via the G4 build-in commands of |
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51 | ParticleGun class (see the macros provided with this example). |
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52 | |
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53 | 4- PHYSICS |
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54 | |
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55 | This example uses the following physics processes: |
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56 | |
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57 | - electromagnetic: |
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58 | photo-electric effect |
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59 | Compton scattering |
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60 | pair production |
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61 | bremsstrahlung |
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62 | ionization |
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63 | multiple scattering |
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64 | annihilation |
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65 | or |
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66 | - polarized electromagnetic: |
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67 | (incl. simulation of polarization transfer, and |
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68 | asymmetries for longitudinally polarized leptons, and |
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69 | circularly polarized photons) |
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70 | |
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71 | polarized photo-electric effect |
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72 | polarized Compton scattering |
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73 | polarized pair production |
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74 | polarized bremsstrahlung |
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75 | polarized ionization |
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76 | multiple scattering |
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77 | polarized annihilation |
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78 | and |
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79 | - transportation |
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80 | |
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81 | and defines the following particles: |
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82 | electron, positron, photon |
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83 | |
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84 | |
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85 | 5- HISTOGRAMS |
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86 | |
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87 | The test contains 12 built-in 1D histograms, which are managed by the |
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88 | HistoManager class and its Messenger. The histos can be individually |
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89 | activated with the command : |
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90 | /testem/histo/setHisto id nbBins valMin valMax unit |
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91 | where unit is the desired unit for the histo (MeV or keV, etc..) |
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92 | (see the macro histos.mac). |
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93 | |
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94 | 1 gamma energy |
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95 | 2 gamma cos(theta) |
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96 | 3 gamma phi |
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97 | 4 gamma polarization |
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98 | 5 electron energy |
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99 | 6 electron cos(theta) |
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100 | 7 electron phi |
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101 | 8 electron polarization |
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102 | 9 positron energy |
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103 | 10 positron cos(theta) |
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104 | 11 positron phi |
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105 | 12 positron polarization |
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106 | |
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107 | If AIDA is available, i.e. if G4ANALYSIS_USE is set, these |
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108 | histograms are stored in a compressed XML file |
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109 | (pol01.aida). These results can be displayed using a small |
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110 | program (plotResults.java) based on JAIDA by simply calling |
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111 | |
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112 | % gmake plots |
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113 | |
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114 | 6- VISUALIZATION |
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115 | |
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116 | Simulated events can be displayed on top of a representation of |
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117 | the geometry, see vis.mac for an example. |
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118 | |
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119 | 7- HOW TO START ? |
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120 | |
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121 | compile and link to generate an executable |
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122 | % gmake |
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123 | |
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124 | execute pol01 in 'batch' mode from the default macro file : |
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125 | % pol01 pol01.in |
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126 | |
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127 | or execute pol01 in 'batch' mode including aida output : |
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128 | % pol01 histos.mac |
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129 | |
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130 | if available use JAIDA to display the results via |
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131 | % gmake plots |
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132 | |
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133 | a visualisation example is available by calling |
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134 | % pol01 |
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135 | [...] |
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136 | PreInit> /control/execute vis.mac |
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