1 | $Id: README,v 1.17 2008/09/18 16:42:07 maire 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 | TestEm6 |
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9 | ------- |
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10 | This example is intended to test the processes of gamma conversion |
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11 | to a pair of muons and annihilation of positrons with atomic |
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12 | electrons to a pair of muons. |
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13 | To make these process more visible, the usually much more frequent |
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14 | gamma conversion to a pair of electrons and the standard positron |
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15 | processes are not selected in the physics list. |
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16 | |
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17 | 1- GEOMETRY DEFINITION |
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18 | |
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19 | The geometry consists of a single block of a homogenous material. |
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20 | |
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21 | Two parameters define the geometry : |
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22 | - the material of the box, |
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23 | - the (full) size of the box. |
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24 | The default is 500 m of iron. |
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25 | |
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26 | In addition a transverse uniform magnetic field can be applied. |
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27 | |
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28 | The default geometry is constructed in DetectorConstruction class, |
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29 | but all of the above parameters can be changed interactively via |
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30 | the commands defined in the DetectorMessenger class. |
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31 | |
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32 | 2- PHYSICS LIST |
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33 | |
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34 | The particle list is the one of novice/exampleN03. |
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35 | The physics list contains the 'standard' electromagnetic processes, |
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36 | and decay. |
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37 | |
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38 | For Gamma, only the GammaConversionToMuons has been registered. |
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39 | Futhermore, a high production cut (1 km, which gives infinity in energy) |
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40 | prevent any production of delta-electrons from ionization or gamma |
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41 | from bremsstrahlung. |
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42 | For Positrons, only the annihilation process is selected. |
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43 | |
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44 | |
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45 | 3- AN EVENT : THE PRIMARY GENERATOR |
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46 | |
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47 | The primary kinematic consists of a single particle which hits the |
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48 | block perpendicular to the input face. The type of the particle |
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49 | and its energy are set in the PrimaryGeneratorAction class, and can |
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50 | changed via the G4 build-in commands of ParticleGun class (see |
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51 | the macros provided with this example). |
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52 | The default is a Gamma of 100 TeV. |
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53 | |
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54 | In addition one can choose randomly the impact point of the incident |
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55 | particle. The corresponding interactive command is built in |
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56 | PrimaryGeneratorMessenger class. |
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57 | |
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58 | A RUN is a set of events. |
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59 | |
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60 | |
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61 | 4- VISUALIZATION |
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62 | |
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63 | The Visualization Manager is set in the main(). |
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64 | The initialisation of the drawing is done via the command |
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65 | > /control/execute vis.mac |
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66 | |
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67 | The detector has a default view which is a longitudinal view of the box. |
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68 | |
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69 | The tracks are drawn at the end of event, and erased at the end of run. |
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70 | Optionaly one can choose to draw all particles, only the charged one, |
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71 | or none. This command is defined in EventActionMessenger class. |
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72 | |
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73 | 5- PHYSICS DEMO |
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74 | |
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75 | The particle's type and the physic processes which will be available |
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76 | in this example are set in PhysicsList class. |
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77 | |
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78 | In addition a build-in interactive command (/process/inactivate proname) |
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79 | allows to activate/inactivate the processes one by one. |
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80 | |
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81 | The threshold for producing secondaries can be changed. |
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82 | eg: /run/particle/setCut 100 micrometer |
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83 | /run/initialize |
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84 | |
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85 | To visualize the GammaConversionToMuons : |
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86 | /control/execute run01.mac |
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87 | /control/execute vis.mac |
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88 | /run/beamOn |
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89 | |
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90 | To visualize the AnnihiToMuPair : |
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91 | /control/execute run11.mac |
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92 | /control/execute vis.mac |
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93 | /run/beamOn |
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94 | |
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95 | 6- HOW TO START ? |
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96 | |
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97 | - compile and link to generate an executable |
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98 | % cd geant4/examples/extended/electromagnetic/TestEm6 |
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99 | % gmake |
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100 | |
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101 | - execute Test in 'batch' mode from macro files |
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102 | % TestEm6 run01.mac |
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103 | |
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104 | - execute Test in 'interactive mode' with visualization |
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105 | % TestEm6 |
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106 | .... |
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107 | Idle> type your commands |
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108 | .... |
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109 | Idle> exit |
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110 | |
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111 | 7- HOW TO INCREASE STATISTICS ON gamma -> mu+mu- ? |
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112 | |
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113 | The processes of gamma -> mu+mu- and e+e- -> mu+mu- |
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114 | have a low cross section but can be important |
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115 | for leakage through thick absorbers and calorimeters. |
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116 | Straight forward simulation will be quite time consuming. |
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117 | To make the processes more visible, the cross section can be |
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118 | artificially increased by some factor (here 1000) |
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119 | using the commands (only effective after /run/initialize) |
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120 | |
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121 | /testem/phys/SetGammaToMuPairFac 1000 |
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122 | /testem/phys/SetAnnihiToMuPairFac 1000 |
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123 | |
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124 | |
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125 | 8- HISTOGRAMS |
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126 | |
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127 | Testem6 produces 6 histograms which illustrate the final state of |
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128 | the GammaConversionToMuons process. See their definitions in RunAction.cc |
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129 | |
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130 | By default the histograms are not activated. To activate histograms |
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131 | the environment variable G4ANALYSIS_USE should be defined. For instance |
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132 | uncomment the flag G4ANALYSIS_USE in GNUmakefile. |
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133 | |
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134 | Before compilation of the example it is optimal to clean up old files: |
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135 | gmake histclean |
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136 | gmake |
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137 | |
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138 | By default the histograms are saved as testem6.root |
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139 | It is possible to choose the format of the histogram file (hbook, root, XML): |
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140 | comment/uncomment 1 line in the constructor of RunAction. |
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141 | |
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142 | To use histograms, at least one of the AIDA implementations should be |
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143 | available. See InstallAida.txt |
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