[1337] | 1 | $Id: README,v 1.10 2009/11/21 00:22:55 perl Exp $ |
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[807] | 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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[1337] | 12 | enabled, as well as event display and analysis. |
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[807] | 13 | |
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| 14 | |
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| 15 | 1. GEOMETRY |
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| 16 | |
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| 17 | The spectrometer consists of two detector arms. One arm provides |
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| 18 | position and timing information of the incident particle while the |
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| 19 | other collects position, timing and energy information of the particle |
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| 20 | after it has been deflected by a magnetic field centered at the |
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| 21 | spectrometer pivot point. |
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| 22 | |
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| 23 | - First arm: box filled with air, also containing: |
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| 24 | |
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| 25 | 1 hodoscope (15 vertical strips of plastic scintillator) |
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| 26 | 1 drift chamber (5 horizontal argon gas layers with a |
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| 27 | "virtual wire" at the center of each layer) |
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| 28 | |
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| 29 | - Magnetic field region: air-filled cylinder which contains |
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| 30 | the field |
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| 31 | |
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| 32 | - Second arm: box filled with air, also containing: |
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| 33 | |
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| 34 | 1 hodoscope (25 vertical strips of plastic scintillator) |
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| 35 | 1 drift chamber (5 horizontal argon gas layers with a |
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| 36 | "virtual wire" at the center of each layer) |
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| 37 | 1 electromagnetic calorimeter: |
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| 38 | a box sub-divided along x,y and z |
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| 39 | axes into cells of CsI |
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| 40 | 1 hadronic calorimeter: |
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| 41 | a box sub-divided along x,y, and z axes |
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| 42 | into cells of lead, with a layer of |
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| 43 | plastic scintillator placed at the center |
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| 44 | of each cell |
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| 45 | |
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| 46 | |
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| 47 | 2. PHYSICS |
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| 48 | |
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| 49 | This example uses the following physics processes: |
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| 50 | |
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| 51 | - electromagnetic: |
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| 52 | photo-electric effect |
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| 53 | Compton scattering |
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| 54 | pair production |
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| 55 | bremsstrahlung |
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| 56 | ionization |
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| 57 | multiple scattering |
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| 58 | annihilation |
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| 59 | |
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| 60 | - decay |
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| 61 | |
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| 62 | - transportation in a field |
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| 63 | |
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| 64 | and defines the following particles: |
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| 65 | geantino, charged geantino, gamma, all leptons, |
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| 66 | pions, charged kaons |
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| 67 | |
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| 68 | Note that even though hadrons are defined, no hadronic processes |
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| 69 | are invoked in this example. |
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| 70 | |
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| 71 | |
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| 72 | 3. EVENT: |
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| 73 | |
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| 74 | An event consists of the generation of a single particle which is |
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| 75 | transported through the first spectrometer arm. Here, a scintillator |
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| 76 | hodoscope records the reference time of the particle before it passes |
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| 77 | through a drift chamber where the particle position is measured. |
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| 78 | Momentum analysis is performed as the particle passes through a magnetic |
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| 79 | field at the spectrometer pivot and then into the second spectrometer |
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| 80 | arm. In the second arm, the particle passes through another hodoscope |
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| 81 | and drift chamber before interacting in the electromagnetic calorimeter. |
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| 82 | Here it is likely that particles will induce electromagnetic showers. |
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| 83 | The shower energy is recorded in a three-dimensional array of CsI |
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| 84 | crystals. Secondary particles from the shower, as well as primary |
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| 85 | particles which do not interact in the CsI crystals, pass into the |
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| 86 | hadronic calorimeter. Here, the remaining energy is collected in a |
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| 87 | three-dimensional array of scintillator-lead sandwiches. |
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| 88 | |
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| 89 | Several aspects of the event may be changed interactively by the user: |
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| 90 | |
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| 91 | - initial particle type |
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| 92 | - initial momentum and angle |
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| 93 | - momentum and angle spreads |
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| 94 | - type of initial particle may be randomized |
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| 95 | - strength of magnetic field |
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| 96 | - angle of the second spectrometer arm |
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| 97 | |
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| 98 | |
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| 99 | 4. DETECTOR RESPONSE: |
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| 100 | |
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| 101 | All the information required to simulate and analyze an event is |
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| 102 | recorded in HITS. This information is recorded in the following |
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| 103 | sensitive detectors: |
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| 104 | |
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| 105 | - hodoscope: |
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| 106 | particle time |
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| 107 | particle position |
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| 108 | strip ID |
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| 109 | |
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| 110 | - drift chamber: |
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| 111 | particle time |
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| 112 | particle position |
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| 113 | layer ID |
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| 114 | |
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| 115 | - electromagnetic calorimeter: |
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| 116 | particle position |
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| 117 | energy deposited in cell |
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| 118 | cell ID |
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| 119 | |
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| 120 | - hadronic calorimeter: |
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| 121 | particle position |
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| 122 | energy deposited in cell |
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| 123 | cell ID |
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| 124 | |
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| 125 | |
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| 126 | 5. VISUALIZATION: |
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| 127 | |
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[1337] | 128 | Simulated events can be displayed on top of a representation of the spectrometer. |
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[807] | 129 | |
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[1337] | 130 | vis.mac outputs HepRep version 1 files suitable for viewing in HepRApp or WIRED4. |
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[807] | 131 | Change the /vis/open line from HepRepFile to DAWNFILE to instead |
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| 132 | make .prim files suitable for viewing in DAWN. |
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| 133 | |
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| 134 | heprep2-000-gz.mac outputs a series of gzipped HepRep version 2 files |
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[1337] | 135 | each containing a single event, suitable for viewing in HepRApp or WIRED4 |
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[807] | 136 | |
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| 137 | heprep2zip.mac outputs a single zip file that unzips to a series of |
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| 138 | HepRep version 2 files, each each containing a single event (unzip |
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[1337] | 139 | the single file by hand, then view the resulting individial HepRep files). |
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[807] | 140 | |
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| 141 | heprep2-000-zip.mac outputs a series of zipped HepRep version 2 files |
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[1337] | 142 | each containing a single event (not yet viewable unless you |
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[807] | 143 | explicitly unzip them before viewing). |
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| 144 | |
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| 145 | heprep2.mac outputs a HepRep version 2 file with multiple events |
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[1337] | 146 | appended to a single file in an experimental manner |
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[807] | 147 | |
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| 148 | heprep2gz.mac outputs a HepRep version 2 file with multiple events |
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[1337] | 149 | appended to a single file in an experimental manner |
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[807] | 150 | |
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| 151 | Any of the heprep mac files above with the name bheprep (for instance |
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[1337] | 152 | bheprep2zip.mac) will write a Binary HepRep version 2 file, readable only |
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| 153 | by WIRED4 (not by HepRApp). |
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[807] | 154 | |
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| 155 | |
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| 156 | 6. ANALYSIS: |
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| 157 | |
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| 158 | This example implements an AIDA-compliant analysis system which |
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[1337] | 159 | creates histograms, ntuples and plotters. If you have built Geant4 with |
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| 160 | the option to use anlaysis (answering yes to the appropriate question in |
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| 161 | ./Configure -build), then at the completion of a simulation run, |
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| 162 | a file A01.aida is produced which contains these data structures. |
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| 163 | This file can be used as an input to the Java Analysis Studio (JAS) which allows |
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| 164 | the histograms and ntuples to examined, manipulated, saved and printed. |
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| 165 | For further details, see README.JAIDA. |
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