Gabriele Cosmo
185 lines
6.5 KiB
Plaintext
185 lines
6.5 KiB
Plaintext
$Id: README,v 1.15 2005/11/22 16:58:54 maire Exp $
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-------------------------------------------------------------------
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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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To make these process more visible, the usually much more frequent
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gamma conversion to a pair of electrons and the standard positron
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processes are not selected in the physics list.
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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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The particle list is the one of novice/exampleN03.
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The physics list contains the 'standard' electromagnetic processes,
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and decay.
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For Gamma, only the GammaConversionToMuons has been registered.
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Futhermore, a high production cut (1 km, which gives infinity in energy)
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prevent any production of delta-electrons from ionization or gamma
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from bremsstrahlung.
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For Positrons, only the annihilation process is selected.
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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 ParticleGun 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().
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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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Optionaly one can choose to draw all particles, only the charged one,
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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 physic 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 proname)
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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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- compile and link to generate an executable
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% cd geant4/examples/extended/electromagnetic/TestEm6
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% gmake
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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 not activated. To activate histograms
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the environment variable G4ANALYSIS_USE should be defined. For instance
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uncomment the flag G4ANALYSIS_USE in GNUmakefile.
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Before compilation of the example it is optimal to clean up old files:
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gmake histclean
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gmake
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By default the histograms are saved as testem6.hbook
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It is possible to choose the format of the histogram file (hbook, root, XML):
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comment/uncomment 1 line in the constructor of RunAction.
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To use histograms, at least one of the AIDA implementations should be
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available (see http://aida.freehep.org).
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8a - PI
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A package including AIDA and extended interfaces also using Python is PI,
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available from: http://cern.ch/pi
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Once installed PI or PI-Lite in a specified local area $MYPY, it is required
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to add the installation path to $PATH, i.e. for example, for release 1.2.1 of
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PI:
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setenv PATH ${PATH}:$MYPI/1.2.1/app/releases/PI/PI_1_2_1/rh73_gcc32/bin
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CERN users can use the PATH to the LCG area on AFS.
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Before running the example the command should be issued:
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eval `aida-config --runtime csh`
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8b - OpenScientist
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OpenScientist is available at http://OpenScientist.lal.in2p3.fr.
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You have to "setup" the OpenScientist AIDA implementation before compiling
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(then with G4ANALYSIS_USE set) and running your Geant4 application.
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On UNIX you setup, with a csh flavoured shell :
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csh> source <<OpenScientist install path>/aida-setup.csh
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or with a sh flavoured shell :
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sh> . <<OpenScientist install path>/aida-setup.sh
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On Windows :
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DOS> call <<OpenScientist install path>/aida-setup.bat
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You can use various file formats for writing (AIDA-XML, hbook, root).
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These formats are readable by the Lab onx interactive program
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or the OpenPAW application. See the web pages.
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With OpenPAW, on a run.hbook file, one can view the histograms
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with something like :
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OS> opaw
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opaw> h/file 1 run.hbook ( or opaw> h/file 1 run.aida or run.root)
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opaw> zone 2 2
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opaw> h/plot 1
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opaw> h/plot 2
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