1 | $Id: README,v 1.9 2005/06/01 18:10:15 duns Exp $ |
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2 | |
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3 | ========================================================= |
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4 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP |
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5 | ========================================================= |
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6 | |
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7 | Extended Example A01 |
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8 | -------------------- |
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9 | |
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10 | Example A01 implements a double-arm spectrometer with wire chambers, |
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11 | hodoscopes and calorimeters. Event simulation and collection are |
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12 | enabled, as well as event display and analysis. This example is |
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13 | extensively documented on the Geant4 Workshop Tutorial CD available at: |
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14 | http://geant4.slac.stanford.edu/g4cd/Welcome.html |
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15 | |
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16 | |
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17 | 1. GEOMETRY |
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18 | |
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19 | The spectrometer consists of two detector arms. One arm provides |
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20 | position and timing information of the incident particle while the |
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21 | other collects position, timing and energy information of the particle |
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22 | after it has been deflected by a magnetic field centered at the |
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23 | spectrometer pivot point. |
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24 | |
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25 | - First arm: box filled with air, also containing: |
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26 | |
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27 | 1 hodoscope (15 vertical strips of plastic scintillator) |
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28 | 1 drift chamber (5 horizontal argon gas layers with a |
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29 | "virtual wire" at the center of each layer) |
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30 | |
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31 | - Magnetic field region: air-filled cylinder which contains |
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32 | the field |
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33 | |
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34 | - Second arm: box filled with air, also containing: |
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35 | |
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36 | 1 hodoscope (25 vertical strips of plastic scintillator) |
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37 | 1 drift chamber (5 horizontal argon gas layers with a |
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38 | "virtual wire" at the center of each layer) |
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39 | 1 electromagnetic calorimeter: |
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40 | a box sub-divided along x,y and z |
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41 | axes into cells of CsI |
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42 | 1 hadronic calorimeter: |
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43 | a box sub-divided along x,y, and z axes |
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44 | into cells of lead, with a layer of |
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45 | plastic scintillator placed at the center |
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46 | of each cell |
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47 | |
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48 | |
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49 | 2. PHYSICS |
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50 | |
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51 | This example uses the following physics processes: |
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52 | |
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53 | - electromagnetic: |
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54 | photo-electric effect |
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55 | Compton scattering |
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56 | pair production |
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57 | bremsstrahlung |
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58 | ionization |
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59 | multiple scattering |
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60 | annihilation |
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61 | |
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62 | - decay |
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63 | |
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64 | - transportation in a field |
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65 | |
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66 | and defines the following particles: |
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67 | geantino, charged geantino, gamma, all leptons, |
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68 | pions, charged kaons |
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69 | |
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70 | Note that even though hadrons are defined, no hadronic processes |
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71 | are invoked in this example. |
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72 | |
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73 | |
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74 | |
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75 | |
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76 | 3. EVENT: |
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77 | |
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78 | An event consists of the generation of a single particle which is |
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79 | transported through the first spectrometer arm. Here, a scintillator |
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80 | hodoscope records the reference time of the particle before it passes |
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81 | through a drift chamber where the particle position is measured. |
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82 | Momentum analysis is performed as the particle passes through a magnetic |
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83 | field at the spectrometer pivot and then into the second spectrometer |
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84 | arm. In the second arm, the particle passes through another hodoscope |
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85 | and drift chamber before interacting in the electromagnetic calorimeter. |
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86 | Here it is likely that particles will induce electromagnetic showers. |
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87 | The shower energy is recorded in a three-dimensional array of CsI |
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88 | crystals. Secondary particles from the shower, as well as primary |
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89 | particles which do not interact in the CsI crystals, pass into the |
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90 | hadronic calorimeter. Here, the remaining energy is collected in a |
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91 | three-dimensional array of scintillator-lead sandwiches. |
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92 | |
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93 | Several aspects of the event may be changed interactively by the user: |
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94 | |
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95 | - initial particle type |
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96 | - initial momentum and angle |
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97 | - momentum and angle spreads |
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98 | - type of initial particle may be randomized |
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99 | - strength of magnetic field |
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100 | - angle of the second spectrometer arm |
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101 | |
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102 | |
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103 | 4. DETECTOR RESPONSE: |
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104 | |
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105 | All the information required to simulate and analyze an event is |
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106 | recorded in HITS. This information is recorded in the following |
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107 | sensitive detectors: |
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108 | |
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109 | - hodoscope: |
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110 | particle time |
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111 | particle position |
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112 | strip ID |
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113 | |
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114 | - drift chamber: |
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115 | particle time |
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116 | particle position |
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117 | layer ID |
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118 | |
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119 | - electromagnetic calorimeter: |
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120 | particle position |
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121 | energy deposited in cell |
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122 | cell ID |
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123 | |
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124 | - hadronic calorimeter: |
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125 | particle position |
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126 | energy deposited in cell |
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127 | cell ID |
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128 | |
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129 | |
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130 | 5. VISUALIZATION: |
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131 | |
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132 | Simulated events can be displayed on top of a representation of |
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133 | the spectrometer. |
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134 | |
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135 | vis.mac outputs HepRep version 1 files suitable for viewing in WIRED. |
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136 | Change the /vis/open line from HepRepFile to DAWNFILE to instead |
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137 | make .prim files suitable for viewing in DAWN. |
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138 | |
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139 | heprep2-000-gz.mac outputs a series of gzipped HepRep version 2 files |
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140 | each containing a single event, suitable for viewing in WIRED (there |
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141 | is no need to ungzip them since WIRED can do this itself). |
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142 | |
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143 | heprep2zip.mac outputs a single zip file that unzips to a series of |
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144 | HepRep version 2 files, each each containing a single event (unzip |
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145 | the single file by hand, then view the resulting individial HepRep |
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146 | files in WIRED 3). |
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147 | |
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148 | heprep2-000-zip.mac outputs a series of zipped HepRep version 2 files |
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149 | each containing a single event (not yet viewable in WIRED unless you |
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150 | explicitly unzip them before viewing). |
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151 | |
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152 | heprep2.mac outputs a HepRep version 2 file with multiple events |
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153 | appended to a single file in an experimental manner (not yet viewable |
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154 | in WIRED). |
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155 | |
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156 | heprep2gz.mac outputs a HepRep version 2 file with multiple events |
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157 | appended to a single file in an experimental manner (not yet viewable |
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158 | in WIRED). |
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159 | |
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160 | Any of the heprep mac files above with the name bheprep (for instance |
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161 | bheprep2zip.mac) will write a Binary HepRep version 2 file, readable |
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162 | by WIRED 4. |
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163 | |
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164 | WIRED 4 can read Binary HepRep and XML HepRep version 2 files without |
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165 | the need for manual unzipping. |
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166 | |
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167 | For more information on visualization with this A01 example, |
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168 | see the visualization tutorials on the Geant4 Workshop Tutorial CD |
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169 | available at: |
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170 | http://geant4.slac.stanford.edu/g4cd/Welcome.html |
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171 | |
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172 | 6. ANALYSIS: |
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173 | |
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174 | This example implements an AIDA-compliant analysis system which |
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175 | creates histograms, ntuples and plotters. At the completion of a |
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176 | simulation run a file A01.aida is produced which contains these |
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177 | data structures. This file can be used as an input to the Java |
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178 | Analysis Studio (JAS) which allows the histograms and ntuples to |
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179 | examined, manipulated, saved and printed. For further details, |
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180 | see README.JAIDA. |
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181 | |
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182 | |
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183 | 7. GETTING STARTED: |
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184 | |
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185 | Build the A01 executable: |
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186 | |
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187 | cd to A01 |
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188 | gmake clean |
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189 | gmake |
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190 | |
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191 | gmake will create tmp and bin directories in your work directory. |
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192 | The executable, named A01app, will be in /bin/$G4SYSTEM/ |
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193 | |
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194 | While in directory A01, run the executable: |
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195 | |
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196 | ../bin/$G4SYSTEM/A01app |
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197 | |
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198 | which will bring up the interactive prompt: |
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199 | |
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200 | Idle> |
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201 | |
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202 | To run 10 events you can now enter: |
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203 | |
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204 | /run/beamOn 10 |
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205 | |
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206 | If all goes well, a JAS window will appear containing two histograms |
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207 | and three scatterplots. |
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208 | |
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209 | To terminate the job, at the prompt enter: |
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210 | |
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211 | exit |
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212 | |
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213 | Currently you must also close the JAS-AIDA window to get the job to stop. |
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214 | |
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215 | |
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216 | In the A01 directory will be a file A01.aida which contains the plots. |
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217 | To examine them |
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218 | |
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219 | /usr/local.bin/jas3 & or jas3 & |
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