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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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TestEm2
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How to do shower profiles in an homogenous medium, with virtual
voxelisation.
1- GEOMETRY DEFINITION
The geometry consists of a cylinder of homogenous material.
The default geometry is constructed in DetectorConstruction class,
but all of the above parameters can be modified interactively via
the commands defined in the DetectorMessenger class.
Material can be choosen: Air Water lAr Al Fe BGO PbWO4 Pb.
eg: /testem/det/setMat PbWO4
The cylinder is virtually sliced longitudinally (slice) and radially
(ring). The size of the slices and rings are expressed in radiation
length units and can be changed.
eg: /testem/det/setLbin 20 1. ---> 20 slices of 1. radl
/testem/det/setRbin 5 0.25 ---> 5 rings of 0.25 radl
/testem/det/update ---> rebuild the geometry
(MaxBin = 500 in both directions)
An uniform magnetic field along the cylinder axis can be set.
eg: /globalField/setValue 0 0 5 tesla
2- PHYSICS LISTS
Physics lists are based on modular design. Several modules are instantiated:
1. Transportation
2. EM physics
3. Decays
4. StepMax - for step limitation
EM physics builders can be local (eg. in this example) or from G4 kernel
physics_lists subdirectory.
Local physics builders:
- "local" standard EM physics with current 'best' options setting.
these options are explicited in PhysListEmStandard
From geant4/source/physics_lists/builders:
- "emstandard_opt0" recommended standard EM physics for LHC
- "emstandard_opt1" best CPU performance standard physics for LHC
- "emstandard_opt2" similar fast simulation
- "emstandard_opt3" best standard EM options - analog to "local" above
- "emstandard_opt4" best current advanced EM options standard + lowenergy
- "emstandardWVI" standard EM physics and WentzelVI multiple scattering
- "emstandardSS" standard EM physics and single scattering model
- "emlivermore" low-energy EM physics using Livermore data
- "empenelope" low-energy EM physics implementing Penelope models
- "emlowenergy" low-energy EM physics implementing experimental
low-energy models
Physics lists and options can be (re)set with UI commands
Please, notice that options set through G4EmProcessOptions are global, eg
for all particle types. In G4 builders, it is shown how to set options per
particle type.
3- AN EVENT : THE PRIMARY GENERATOR
The primary kinematic consists of a single particle which hits the
cylinder perpendicular to the input face. The type of the particle
and its energy are set in the PrimaryGeneratorAction class, and can
changed via the G4 build-in commands of G4ParticleGun class (see
the macros provided with this example).
A RUN is a set of events.
4- VISUALIZATION
The Visualization Manager is set in the main() (see TestEm2.cc).
The initialisation of the drawing is done via the commands
/vis/.. in the macro vis.mac. In interactive session:
PreInit or Idle > /control/execute vis.mac
The detector has a default view which is a longitudinal view of the
cylinder.
The tracks are drawn at the end of event, and erased at the end of run.
Optionally one can choose to draw all particles, only the charged one,
or none. This command is defined in EventActionMessenger class.
5- PHYSICS DEMO
The particle's type and the physics processes which will be available
in this example are set in PhysicsList class.
In addition a build-in interactive command (/process/inactivate procname)
allows to activate/inactivate the processes one by one.
The threshold for producing secondaries can be changed.
eg: /testem/phys/setCuts 100 microm
/run/initialize
The shower profiles are histogramed, if histograming is activated.
They can be also printed with the command /testem/run/verbose 1
6- HOW TO START ?
- Execute TestEm2 in 'batch' mode from macro files
% TestEm2 run01.mac
- Execute TestEm2 in 'batch' mode using multi-threading
% TestEm2 run01.mac 4
here 4 is number of threads, it should be user defined,
optimal value depends on hardware
- Execute TestEm2 in 'interactive mode' with visualization
% TestEm2
....
Idle> type your commands
....
Idle> exit
Macros provided in this example:
- egs4.mac:
Fe; L = 20 radl; R = 5 radl; electron 30 GeV
(EGS4 simulation: Particle Data Group - Phys.Rev.D 50-3 - August94)
- run01.mac: PbWO4; L = 20 radl; R = 5 radl; electron 5 GeV
- run02.mac: Al; L = 13.5 radl; R = 1.35 radl; electron 1 GeV
(Electron-induced cascade showers: J&H Crannel - Phys. Rev. 184-2 - August69)
- run03.mac: H2O; L = 9.97 radl; R = 0.665 radl; electron 1 GeV
(Electron-induced cascade showers: J&H Crannel - Phys. Rev. 184-2 - August69)
- test.mac: PbWO4; L = 20 radl; R = 5 radl; electron 5 GeV
- vis.mac: to activate visualization
7- HISTOGRAMS
TestEm2 produces several histograms:
Content of these histo:
1 : energy deposit per event
2 : charged track length per event
3 : neutral track length per event
4 : longitudinal energy profile
5 : rms of longitudinal energy profile
6 : cumulated longitudinal energy profile
7 : rms of cumulated longitudinal energy profile
8 : radial energy profile
9 : rms of radial energy profile
10 : cumulated radial energy profile
11 : rms of cumulated radial energy profile
To define the output file name with histograms, use the UI command :
"/analysis/setFileName name"
The format of the histogram file can be : root (default),
xml, csv, by selecting g4nnn.hh in RunAction.hh
Gabriele Cosmo