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1 -------------------------------------------------------------------
2
3 =========================================================
4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
5 =========================================================
6
7 Example B2
8 ----------
9
10 This example simulates a simplified fixed target experiment.
11
12 1- GEOMETRY DEFINITION
13
14 The setup consists of a target followed by six chambers of increasing
15 transverse size at defined instances from the target. These chambers are
16 located in a region called the Tracker region.
17 Their shape are cylinders, constructed as simple cylinders
18 (in B2a::DetectorConstruction) and as parametrised volumes
19 (in B2b::DetectorConstruction), see also B2b::ChamberParameterisation class.
20
21 In addition, a global, uniform, and transverse magnetic field can be
22 applied using G4GlobalMagFieldMessenger, instantiated in
23 B2[a,b]::DetectorConstruction::ConstructSDandField with a non zero field value,
24 or via interactive commands.
25 For example:
26
27 /globalField/setValue 0.2 0 0 tesla
28
29 An instance of the B2::TrackerSD class is created and associated with each
30 logical chamber volume (in B2a) and with the one G4LogicalVolume associated
31 with G4PVParameterised (in B2b).
32
33 One can change the materials of the target and the chambers
34 interactively via the commands defined in B2a::DetectorMessenger
35 (or B2b::DetectorMessenger). For example:
36
37 /B2/det/setTargetMaterial G4_WATER
38 /B2/det/setChamberMaterial G4_Ar
39
40 2- PHYSICS LIST
41
42 The particle's type and the physic processes which will be available
43 in this example are set in the FTFP_BERT physics list. This physics list
44 requires data files for electromagnetic and hadronic processes.
45 See more on installation of the datasets in Geant4 Installation Guide,
46 Chapter 3.3: Note On Geant4 Datasets:
47 http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/InstallationGuide/html/ch03s03.html
48 The following datasets: G4LEDATA, G4LEVELGAMMADATA, G4SAIDXSDATA and
49 G4ENSDFSTATEDATA are mandatory for this example.
50
51 In addition, the build-in interactive command:
52 /process/(in)activate processName
53 allows the user to activate/inactivate the processes one by one.
54
55 3- ACTION INITALIZATION
56
57 A newly introduced class, B2::ActionInitialization,
58 instantiates and registers to Geant4 kernel all user action classes.
59
60 While in sequential mode the action classes are instatiated just once,
61 via invoking the method:
62 B2::ActionInitialization::Build()
63 in multi-threading mode the same method is invoked for each thread worker
64 and so all user action classes are defined thread-local.
65
66 A run action class is instantiated both thread-local
67 and global that's why its instance has is created also in the method
68 B2::ActionInitialization::BuildForMaster()
69 which is invoked only in multi-threading mode.
70
71 4- PRIMARY GENERATOR
72
73 The primary generator action class employs the G4ParticleGun.
74 The primary kinematics consists of a single particle which starts close
75 to the world boundary and hits the target perpendicular to the entrance
76 face. The type of the particle and its energy can be changed via the
77 Geant4 built-in commands of the G4ParticleGun class.
78
79 5- RUNS and EVENTS
80
81 A run is a set of events.
82
83 The user has control:
84 - at Begin and End of each run (class B2::RunAction)
85 - at Begin and End of each event (class B2::EventAction)
86 - at Begin and End of each track (class TrackingAction, not used here)
87 - at End of each step (class SteppingAction, not used here)
88
89 The event number is written to the log file every requested number
90 of events in B2::EventAction::BeginOfEventAction() and
91 B2::EventAction::EndOfEventAction().
92 Moreover, for the first 100 events and every 100 events thereafter
93 information about the number of stored trajectories in the event
94 is printed as well as the number of hits stored in the G4VHitsCollection.
95
96 The run number is printed at B2::RunAction::BeginOfRunAction(), where the
97 G4RunManager is also informed how to SetRandomNumberStore for storing
98 initial random number seeds per run or per event.
99
100 6- USER LIMITS
101
102 This example also illustrates how to introduce tracking constraints
103 like maximum step length, minimum kinetic energy etc. via the G4UserLimits
104 class and associated G4StepLimiter and G4UserSpecialCuts processes.
105 See B2a::DetectorConstruction (or B2b::DetectorConstruction).
106
107 The maximum step limit in the tracker region can be set by the interactive
108 command (see B2a::DetectorMessenger, B2b::DetectorMessenger classes).
109 For example:
110
111 /B2/det/stepMax 1.0 mm
112
113 7- DETECTOR RESPONSE
114
115 A HIT is a step per step record of all the information needed to
116 simulate and analyse the detector response.
117
118 In this example the Tracker chambers are considered to be the detector.
119 Therefore, the chambers are declared 'sensitive detectors' (SD) in
120 the B2a::DetectorConstruction (or B2b::DetectorConstruction) class.
121 They are associated with an instance of the B2::TrackerSD class.
122
123 Then, a Hit is defined as a set of 4 informations per step, inside
124 the chambers, namely:
125 - the track identifier (an integer),
126 - the chamber number,
127 - the total energy deposit in this step, and
128 - the position of the energy deposit.
129
130 A given hit is an instance of the class B2::TrackerHit which is created
131 during the tracking of a particle, step by step, in the method
132 B2::TrackerSD::ProcessHits(). This hit is inserted in a HitsCollection.
133
134 The HitsCollection is printed at the end of each event (via the method
135 B2::TrackerSD::EndOfEvent()), under the control of the command:
136 /hits/verbose 2
137
138 The following paragraphs are common to all basic examples
139
140 A- VISUALISATION
141
142 The visualization manager is set via the G4VisExecutive class
143 in the main() function in exampleB2a.cc (or exampleB2b.cc).
144 The initialisation of the drawing is done via a set of /vis/ commands
145 in the macro vis.mac. This macro is automatically read from
146 the main function when the example is used in interactive running mode.
147
148 By default, vis.mac opens an OpenGL viewer (/vis/open OGL).
149 The user can change the initial viewer by commenting out this line
150 and instead uncommenting one of the other /vis/open statements, such as
151 HepRepFile or DAWNFILE (which produce files that can be viewed with the
152 HepRApp and DAWN viewers, respectively). Note that one can always
153 open new viewers at any time from the command line. For example, if
154 you already have a view in, say, an OpenGL window with a name
155 "viewer-0", then
156 /vis/open DAWNFILE
157 then to get the same view
158 /vis/viewer/copyView viewer-0
159 or to get the same view *plus* scene-modifications
160 /vis/viewer/set/all viewer-0
161 then to see the result
162 /vis/viewer/flush
163
164 The DAWNFILE, HepRepFile drivers are always available
165 (since they require no external libraries), but the OGL driver requires
166 that the Geant4 libraries have been built with the OpenGL option.
167
168 Since 11.1, the TSG visualization driver can also produce the "offscrean"
169 file output in png, jpeg, gl2ps formats without drawing on the screen.
170 It can be controlled via UI commands provided in '/vis/tsg' which are
171 demonstrated in the tsg_offscreen.mac macro in example B5.
172
173 For more information on visualization, including information on how to
174 install and run DAWN, OpenGL and HepRApp, see the visualization tutorials,
175 for example,
176 http://geant4.slac.stanford.edu/Presentations/vis/G4[VIS]Tutorial/G4[VIS]Tutorial.html
177 (where [VIS] can be replaced by DAWN, OpenGL and HepRApp)
178
179 The tracks are automatically drawn at the end of each event, accumulated
180 for all events and erased at the beginning of the next run.
181
182 B- USER INTERFACES
183
184 The user command interface is set via the G4UIExecutive class
185 in the main() function in exampleB2a.cc
186
187 The selection of the user command interface is then done automatically
188 according to the Geant4 configuration or it can be done explicitly via
189 the third argument of the G4UIExecutive constructor (see exampleB4a.cc).
190
191 The gui.mac macros are provided in examples B2, B4 and B5. This macro
192 is automatically executed if Geant4 is built with any GUI session.
193 It is also possible to customise the icons menu bar which is
194 demonstrated in the icons.mac macro in example B5.
195
196 C- HOW TO RUN
197
198 - Execute exampleB2a in the 'interactive mode' with visualization
199 % exampleB2a
200 and type in the commands from run1.mac line by line:
201 Idle> /tracking/verbose 1
202 Idle> /run/beamOn 1
203 Idle> ...
204 Idle> exit
205 or
206 Idle> /control/execute run1.mac or run2.mac
207 ....
208 Idle> exit
209
210 - Execute exampleB2a in the 'batch' mode from macro files
211 (without visualization)
212 % exampleB2a run2.mac
213 % exampleB2a exampleB2.in > exampleB2.out
214
