1 | $Id: README,v 1.10 2009/11/21 00:22:55 perl Exp $ |
---|
2 | |
---|
3 | ========================================================= |
---|
4 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP |
---|
5 | ========================================================= |
---|
6 | |
---|
7 | Extended Example A01 |
---|
8 | -------------------- |
---|
9 | |
---|
10 | Example A01 implements a double-arm spectrometer with wire chambers, |
---|
11 | hodoscopes and calorimeters. Event simulation and collection are |
---|
12 | enabled, as well as event display and analysis. |
---|
13 | |
---|
14 | |
---|
15 | 1. GEOMETRY |
---|
16 | |
---|
17 | The spectrometer consists of two detector arms. One arm provides |
---|
18 | position and timing information of the incident particle while the |
---|
19 | other collects position, timing and energy information of the particle |
---|
20 | after it has been deflected by a magnetic field centered at the |
---|
21 | spectrometer pivot point. |
---|
22 | |
---|
23 | - First arm: box filled with air, also containing: |
---|
24 | |
---|
25 | 1 hodoscope (15 vertical strips of plastic scintillator) |
---|
26 | 1 drift chamber (5 horizontal argon gas layers with a |
---|
27 | "virtual wire" at the center of each layer) |
---|
28 | |
---|
29 | - Magnetic field region: air-filled cylinder which contains |
---|
30 | the field |
---|
31 | |
---|
32 | - Second arm: box filled with air, also containing: |
---|
33 | |
---|
34 | 1 hodoscope (25 vertical strips of plastic scintillator) |
---|
35 | 1 drift chamber (5 horizontal argon gas layers with a |
---|
36 | "virtual wire" at the center of each layer) |
---|
37 | 1 electromagnetic calorimeter: |
---|
38 | a box sub-divided along x,y and z |
---|
39 | axes into cells of CsI |
---|
40 | 1 hadronic calorimeter: |
---|
41 | a box sub-divided along x,y, and z axes |
---|
42 | into cells of lead, with a layer of |
---|
43 | plastic scintillator placed at the center |
---|
44 | of each cell |
---|
45 | |
---|
46 | |
---|
47 | 2. PHYSICS |
---|
48 | |
---|
49 | This example uses the following physics processes: |
---|
50 | |
---|
51 | - electromagnetic: |
---|
52 | photo-electric effect |
---|
53 | Compton scattering |
---|
54 | pair production |
---|
55 | bremsstrahlung |
---|
56 | ionization |
---|
57 | multiple scattering |
---|
58 | annihilation |
---|
59 | |
---|
60 | - decay |
---|
61 | |
---|
62 | - transportation in a field |
---|
63 | |
---|
64 | and defines the following particles: |
---|
65 | geantino, charged geantino, gamma, all leptons, |
---|
66 | pions, charged kaons |
---|
67 | |
---|
68 | Note that even though hadrons are defined, no hadronic processes |
---|
69 | are invoked in this example. |
---|
70 | |
---|
71 | |
---|
72 | 3. EVENT: |
---|
73 | |
---|
74 | An event consists of the generation of a single particle which is |
---|
75 | transported through the first spectrometer arm. Here, a scintillator |
---|
76 | hodoscope records the reference time of the particle before it passes |
---|
77 | through a drift chamber where the particle position is measured. |
---|
78 | Momentum analysis is performed as the particle passes through a magnetic |
---|
79 | field at the spectrometer pivot and then into the second spectrometer |
---|
80 | arm. In the second arm, the particle passes through another hodoscope |
---|
81 | and drift chamber before interacting in the electromagnetic calorimeter. |
---|
82 | Here it is likely that particles will induce electromagnetic showers. |
---|
83 | The shower energy is recorded in a three-dimensional array of CsI |
---|
84 | crystals. Secondary particles from the shower, as well as primary |
---|
85 | particles which do not interact in the CsI crystals, pass into the |
---|
86 | hadronic calorimeter. Here, the remaining energy is collected in a |
---|
87 | three-dimensional array of scintillator-lead sandwiches. |
---|
88 | |
---|
89 | Several aspects of the event may be changed interactively by the user: |
---|
90 | |
---|
91 | - initial particle type |
---|
92 | - initial momentum and angle |
---|
93 | - momentum and angle spreads |
---|
94 | - type of initial particle may be randomized |
---|
95 | - strength of magnetic field |
---|
96 | - angle of the second spectrometer arm |
---|
97 | |
---|
98 | |
---|
99 | 4. DETECTOR RESPONSE: |
---|
100 | |
---|
101 | All the information required to simulate and analyze an event is |
---|
102 | recorded in HITS. This information is recorded in the following |
---|
103 | sensitive detectors: |
---|
104 | |
---|
105 | - hodoscope: |
---|
106 | particle time |
---|
107 | particle position |
---|
108 | strip ID |
---|
109 | |
---|
110 | - drift chamber: |
---|
111 | particle time |
---|
112 | particle position |
---|
113 | layer ID |
---|
114 | |
---|
115 | - electromagnetic calorimeter: |
---|
116 | particle position |
---|
117 | energy deposited in cell |
---|
118 | cell ID |
---|
119 | |
---|
120 | - hadronic calorimeter: |
---|
121 | particle position |
---|
122 | energy deposited in cell |
---|
123 | cell ID |
---|
124 | |
---|
125 | |
---|
126 | 5. VISUALIZATION: |
---|
127 | |
---|
128 | Simulated events can be displayed on top of a representation of the spectrometer. |
---|
129 | |
---|
130 | vis.mac outputs HepRep version 1 files suitable for viewing in HepRApp or WIRED4. |
---|
131 | Change the /vis/open line from HepRepFile to DAWNFILE to instead |
---|
132 | make .prim files suitable for viewing in DAWN. |
---|
133 | |
---|
134 | heprep2-000-gz.mac outputs a series of gzipped HepRep version 2 files |
---|
135 | each containing a single event, suitable for viewing in HepRApp or WIRED4 |
---|
136 | |
---|
137 | heprep2zip.mac outputs a single zip file that unzips to a series of |
---|
138 | HepRep version 2 files, each each containing a single event (unzip |
---|
139 | the single file by hand, then view the resulting individial HepRep files). |
---|
140 | |
---|
141 | heprep2-000-zip.mac outputs a series of zipped HepRep version 2 files |
---|
142 | each containing a single event (not yet viewable unless you |
---|
143 | explicitly unzip them before viewing). |
---|
144 | |
---|
145 | heprep2.mac outputs a HepRep version 2 file with multiple events |
---|
146 | appended to a single file in an experimental manner |
---|
147 | |
---|
148 | heprep2gz.mac outputs a HepRep version 2 file with multiple events |
---|
149 | appended to a single file in an experimental manner |
---|
150 | |
---|
151 | Any of the heprep mac files above with the name bheprep (for instance |
---|
152 | bheprep2zip.mac) will write a Binary HepRep version 2 file, readable only |
---|
153 | by WIRED4 (not by HepRApp). |
---|
154 | |
---|
155 | |
---|
156 | 6. ANALYSIS: |
---|
157 | |
---|
158 | This example implements an AIDA-compliant analysis system which |
---|
159 | creates histograms, ntuples and plotters. If you have built Geant4 with |
---|
160 | the option to use anlaysis (answering yes to the appropriate question in |
---|
161 | ./Configure -build), then at the completion of a simulation run, |
---|
162 | a file A01.aida is produced which contains these data structures. |
---|
163 | This file can be used as an input to the Java Analysis Studio (JAS) which allows |
---|
164 | the histograms and ntuples to examined, manipulated, saved and printed. |
---|
165 | For further details, see README.JAIDA. |
---|