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1
2 =========================================================
3 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
4 =========================================================
5
6 Extended Example B5
7 --------------------
8
9 Example B5 implements a double-arm spectrometer with wire chambers,
10 hodoscopes and calorimeters. Event simulation and collection are
11 enabled, as well as event display and analysis.
12
13
14 1- GEOMETRY
15
16 The spectrometer consists of two detector arms
17 (see B5::DetectorConstruction). 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 - Second arm: box filled with air, also containing:
30
31 1 hodoscope (25 vertical strips of plastic scintillator)
32 1 drift chamber (5 horizontal argon gas layers with a
33 "virtual wire" at the center of each layer)
34 1 electromagnetic calorimeter:
35 a box sub-divided along x,y and z
36 axes into cells of CsI
37 1 hadronic calorimeter:
38 a box sub-divided along x,y, and z axes
39 into cells of lead, with a layer of
40 plastic scintillator placed at the center
41 of each cell
42
43 - Magnetic field region: air-filled cylinder which contains
44 the field (see B5::MagneticField)
45
46 The maximum step limit in the magnetic field region is also set
47 via the G4UserLimits class in a similar way as in Example B2.
48
49 The rotation angle of the second arm and the magnetic field value
50 can be set via the interactive command defined using the G4GenericMessenger
51 class.
52
53 2- PHYSICS
54
55 This example uses the reference hadronic physics list, FTFP_BERT,
56 and also adds the G4StepLimiter process.
57
58
59 3- ACTION INITALIZATION
60
61 B5::ActionInitialization class
62 instantiates and registers to Geant4 kernel all user action classes.
63
64 While in sequential mode the action classes are instatiated just once,
65 via invoking the method:
66 B5::ActionInitialization::Build()
67 in multi-threading mode the same method is invoked for each thread worker
68 and so all user action classes are defined thread-local.
69
70 A run action class is instantiated both thread-local
71 and global that's why its instance is created also in the method
72 B5::ActionInitialization::BuildForMaster()
73 which is invoked only in multi-threading mode.
74
75 4- PRIMARY GENERATOR
76
77 The primary generator action class employs the G4ParticleGun.
78 The primary kinematics consists of a single particle which is
79 is sent in the direction of the first spectrometer arm.
80
81 The type of the particle and its several properties can be changed
82 via the G4 built-in commands of the G4ParticleGun class or
83 this example command defined using the G4GenericMessenger class.
84
85
86 5- EVENT
87
88 An event consists of the generation of a single particle which is
89 transported through the first spectrometer arm. Here, a scintillator
90 hodoscope records the reference time of the particle before it passes
91 through a drift chamber where the particle position is measured.
92 Momentum analysis is performed as the particle passes through a magnetic
93 field at the spectrometer pivot and then into the second spectrometer
94 arm. In the second arm, the particle passes through another hodoscope
95 and drift chamber before interacting in the electromagnetic calorimeter.
96 Here it is likely that particles will induce electromagnetic showers.
97 The shower energy is recorded in a three-dimensional array of CsI
98 crystals. Secondary particles from the shower, as well as primary
99 particles which do not interact in the CsI crystals, pass into the
100 hadronic calorimeter. Here, the remaining energy is collected in a
101 three-dimensional array of scintillator-lead sandwiches.
102
103 Several aspects of the event may be changed interactively by the user:
104 - angle of the second spectrometer arm
105 - strength of magnetic field
106 - initial particle type
107 - initial momentum and angle
108 - momentum and angle spreads
109 - type of initial particle may be randomized
110
111 The initial particle type can be changed using the G4ParticleGun command:
112 /gun/particle particleName
113
114 The UI commands specific to this example are available in /B5 command
115 directory:
116 /B5/detector/armAngle angle unit
117 /B5/field/value field unit
118 /B5/generator/momentum value unit
119 /B5/generator/sigmaMomentum value unit
120 /B5/generator/sigmaAngle value unit
121 /B5/generator/randomizePrimary [true|false]
122
123 They are implemented in
124 B5::DetectorConstruction::DefineCommands(),
125 B5::MagneticField::DefineCommands() and
126 B5::PrimaryGeneratorAction::DefineCommands() methods
127 using G4GenericMessenger class.
128
129 In first execution of BeginOfEventAction()
130 the hits collections identifiers are saved in data members of the class
131 and used in EndOfEventAction() for accessing
132 the hists collections and filling the accounted information in defined
133 histograms and ntuples and printing its summary in a log file.
134 The frequency of printing can be tuned with the built-in command
135 /run/printProgress frequency
136
137 6- DETECTOR RESPONSE:
138
139 All the information required to simulate and analyze an event is
140 recorded in hits. This information is recorded in the following
141 sensitive detectors:
142
143 - hodoscope:
144 particle time
145 strip ID, position and rotation
146 (see B5::HodoscopeSD, B5::HodoscopeHit classes)
147
148 - drift chamber:
149 particle time
150 particle position
151 layer ID
152 (see B5::DriftChamberSD, B5::DriftChamberHit classes)
153
154 - electromagnetic calorimeter:
155 energy deposited in cell
156 cell ID, position and rotation
157 (see B5::EMCalorimeterSD, B5::EMCalorimeterHit classes)
158
159 - hadronic calorimeter:
160 energy deposited in cell
161 cell column ID and row ID, position and rotation
162 (see B5::HadCalorimeterSD, B5::HadCalorimeterHit classes)
163
164 The hit classes include methods GetAttDefs and CreateAttValues to define
165 and then fill extra "HepRep-style" Attributes that the visualization system
166 can use to present extra information about the hits.
167 For example, if you pick a B5::HadCalorimeterHit in OpenGL or a HepRep viewer,
168 you will be shown the hit's "Hit Type", "Column ID", "Row ID",
169 "Energy Deposited" and "Position".
170 These attributes are essentially arbitrary extra pieces of information
171 (integers, doubles or strings) that are carried through the visualization.
172 Each attribute is defined once in G4AttDef object and then is filled for
173 each hit in a G4AttValue object.
174 These attributes can also be used by commands to filter which hits are drawn:
175 /vis/filtering/hits/drawByAttribute
176 Detector Geometry and trajectories also carry HepRep-style attributes,
177 but these are filled automatically in the base classes.
178 HepRep is further described at: http://www.slac.stanford.edu/~perl/heprep/
179
180 7- ANALYSIS:
181
182 The analysis tools are used to accumulate statistics.
183 Histograms and an ntuple are created in B5::RunAction::RunAction()
184 constructor for the following quantities:
185
186 1D histograms:
187 - Number of hits in Chamber 1
188 - Number of hits in Chamber 2
189
190 2D histograms:
191 - Drift Chamber 1 X vs Y positions
192 - Drift Chamber 2 X vs Y positions
193
194 Ntuple:
195 - Number of hits in Chamber 1
196 - Number of hits in Chamber 2
197 - Total energy deposit in EM calorimeter
198 - Total energy deposit in Hadronic calorimeter
199 - Time of flight in Hodoscope 1
200 - Time of flight in Hodoscope 2
201 - Vector of energy deposits in EM calorimeter cells
202 - Vector of energy deposits in Hadronic calorimeter cells
203
204 The histograms and ntuple are saved in two output files in a default
205 (Root) file format.
206
207 Another file format (for example xml) can be selected either by
208 changing the generic analysis manager default file type:
209 analysisManager->SetDefaultFileType("xml");
210 or by providing the file names with the extension:
211 analysisManager->SetFileName("B5.xml");
212 analysisManager->SetNtupleFileName(0, "B4ntuple.xml");
213
214 When running in multi-threading mode, the histograms and ntuple accumulated
215 on threads are automatically merged in a single output file.
216
217 8- PLOTTING:
218
219 This example comes with a commented plotter.mac that shows how to use the
220 plotting coming with some of the visualization drivers (for example the
221 ToolsSG ones) to see the histograms. In it you will see how to activate
222 the vis driver (create a "scene handler"), create a viewer, create a scene
223 containing a plotter model object, create plotting "regions" (here 2x2
224 regions) and attach the histograms to each region. When done, each
225 run beamOn should display at end the content of the histograms.
226
227 In the second part of plotter.mac, is shown various ways to customize the
228 regions, for example changing the bins color, the axis labels fonts, etc...
229 This could be done by using default embedded styles, defining styles with commands,
230 or setting up directly parameters of the various parts of a plot by using a
231 dedicated command.
232
233 By default the fonts used are the Hershey vectorial ones that do not need
234 an extra package, but you can use some freetype fonts if building with the
235 cmake flag -DGEANT4_USE_FREETYPE=ON. Two embedded ttf fonts comes with the
236 ToolsSG plotting: roboto_bold (some open source kind of the Microsoft arialbd)
237 and lato_regular (close to an helvetica). You can use your own .ttf files by
238 using the TOOLS_FONT_PATH environment variable to specify the directory where
239 they could be found.
240
241 The following paragraphs are common to all basic examples
242
243 A- VISUALISATION
244
245 The visualization manager is set via the G4VisExecutive class
246 in the main() function in exampleB5.cc.
247 The initialisation of the drawing is done via a set of /vis/ commands
248 in the macro vis.mac. This macro is automatically read from
249 the main function when the example is used in interactive running mode.
250
251 By default, vis.mac opens an OpenGL viewer (/vis/open OGL).
252 The user can change the initial viewer by commenting out this line
253 and instead uncommenting one of the other /vis/open statements, such as
254 HepRepFile or DAWNFILE (which produce files that can be viewed with the
255 HepRApp and DAWN viewers, respectively). Note that one can always
256 open new viewers at any time from the command line. For example, if
257 you already have a view in, say, an OpenGL window with a name
258 "viewer-0", then
259 /vis/open DAWNFILE
260 then to get the same view
261 /vis/viewer/copyView viewer-0
262 or to get the same view *plus* scene-modifications
263 /vis/viewer/set/all viewer-0
264 then to see the result
265 /vis/viewer/flush
266
267 The DAWNFILE, HepRepFile drivers are always available
268 (since they require no external libraries), but the OGL driver requires
269 that the Geant4 libraries have been built with the OpenGL option.
270
271 vis.mac has additional commands that demonstrate additional functionality
272 of the vis system, such as displaying text, axes, scales, date, logo and
273 shows how to change viewpoint and style.
274 To see even more commands use help or ls or browse the available UI commands
275 in the Application Developers Guide.
276
277 For more information on visualization, including information on how to
278 install and run DAWN, OpenGL and HepRApp, see the visualization tutorials,
279 for example,
280 http://geant4.slac.stanford.edu/Presentations/vis/G4[VIS]Tutorial/G4[VIS]Tutorial.html
281 (where [VIS] can be replaced by DAWN, OpenGL and HepRApp)
282
283 The tracks are automatically drawn at the end of each event, accumulated
284 for all events and erased at the beginning of the next run.
285
286 B- USER INTERFACES
287
288 The user command interface is set via the G4UIExecutive class
289 in the main() function in exampleB5.cc
290 The selection of the user command interface is then done automatically
291 according to the Geant4 configuration or it can be done explicitly via
292 the third argument of the G4UIExecutive constructor (see exampleB4a.cc).
293
294 C- HOW TO RUN
295
296 - Execute exampleB5 in the 'interactive mode' with visualization:
297 % ./exampleB5
298 and type in the commands from run1.mac line by line:
299 Idle> /control/verbose 2
300 Idle> /tracking/verbose 1
301 Idle> /run/beamOn 10
302 Idle> ...
303 Idle> exit
304 or
305 Idle> /control/execute run1.mac
306 ....
307 Idle> exit
308
309 - Execute exampleB5 in the 'batch' mode from macro files
310 (without visualization)
311 % ./exampleB5 run2.mac
312 % ./exampleB5 exampleB5.in > exampleB5.out
313
314
