Gabriele Cosmo
126 lines
4.3 KiB
Plaintext
126 lines
4.3 KiB
Plaintext
-------------------------------------------------------------------
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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TestEm6
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-------
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This example is intended to test the processes of gamma conversion
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to a pair of muons and annihilation of positrons with atomic
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electrons to a pair of muons.
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1- GEOMETRY DEFINITION
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The geometry consists of a single block of a homogenous material.
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Two parameters define the geometry :
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- the material of the box,
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- the (full) size of the box.
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The default is 500 m of iron.
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In addition a transverse uniform magnetic field can be applied.
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The default geometry is constructed in DetectorConstruction class,
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but all of the above parameters can be changed interactively via
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the commands defined in the DetectorMessenger class.
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2- PHYSICS LIST
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Physics Lists are based on modular design. Several modules are
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instantiated:
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1. Transportation
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2. EM physics
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3. Decays
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4. StepMax - for step limitation
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The electromagnetic physics is chosen from one of the Geant4 EM
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physics constructors in the physics_list library.
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Cross sections can be enhanced (see below).
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3- AN EVENT : THE PRIMARY GENERATOR
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The primary kinematic consists of a single particle which hits the
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block perpendicular to the input face. The type of the particle
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and its energy are set in the PrimaryGeneratorAction class, and can
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changed via the G4 build-in commands of G4ParticleGun class (see
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the macros provided with this example).
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The default is a Gamma of 100 TeV.
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In addition one can choose randomly the impact point of the incident
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particle. The corresponding interactive command is built in
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PrimaryGeneratorMessenger class.
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A RUN is a set of events.
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4- VISUALIZATION
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The Visualization Manager is set in the main() (see TestEm6.cc).
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The initialisation of the drawing is done via the command
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> /control/execute vis.mac
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The detector has a default view which is a longitudinal view of the box.
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The tracks are drawn at the end of event, and erased at the end of run.
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Optionally one can choose to draw all particles, only the charged ones,
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or none. This command is defined in EventActionMessenger class.
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5- PHYSICS DEMO
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The particle's type and the physics processes which will be available
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in this example are set in PhysicsList class.
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In addition a build-in interactive command (/process/inactivate procname)
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allows to activate/inactivate the processes one by one.
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The threshold for producing secondaries can be changed.
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eg: /run/particle/setCut 100 micrometer
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/run/initialize
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To visualize the GammaConversionToMuons :
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/control/execute run01.mac
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/control/execute vis.mac
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/run/beamOn
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To visualize the AnnihiToMuPair :
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/control/execute run11.mac
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/control/execute vis.mac
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/run/beamOn
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6- HOW TO START ?
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- execute Test in 'batch' mode from macro files
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% TestEm6 run01.mac
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- execute Test in 'interactive mode' with visualization
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% TestEm6
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....
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Idle> type your commands
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....
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Idle> exit
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7- HOW TO INCREASE STATISTICS ON gamma -> mu+mu- ?
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The processes of gamma -> mu+mu- and e+e- -> mu+mu-
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have a low cross section but can be important
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for leakage through thick absorbers and calorimeters.
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Straight forward simulation will be quite time consuming.
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To make the processes more visible, the cross section can be
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artificially increased by some factor (here 1000)
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using the commands (only effective after /run/initialize)
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/testem/phys/SetGammaToMuPairFac 1000
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/testem/phys/SetAnnihiToMuPairFac 1000
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8- HISTOGRAMS
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Testem6 produces 6 histograms which illustrate the final state of
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the GammaConversionToMuons process. See their definitions in RunAction.cc
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By default the histograms are saved as testem6.root
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The format of the histogram file can be : root (default), xml, csv,
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by selecting g4nnn.hh in RunAction.hh
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