| 1 | $Id: README,v 1.17 2008/09/18 16:42:07 maire Exp $
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| 2 | -------------------------------------------------------------------
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| 3 |
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| 4 | =========================================================
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| 5 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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| 6 | =========================================================
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| 7 |
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| 8 | TestEm6
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| 9 | -------
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| 10 | This example is intended to test the processes of gamma conversion
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| 11 | to a pair of muons and annihilation of positrons with atomic
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| 12 | electrons to a pair of muons.
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| 13 | To make these process more visible, the usually much more frequent
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| 14 | gamma conversion to a pair of electrons and the standard positron
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| 15 | processes are not selected in the physics list.
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| 16 |
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| 17 | 1- GEOMETRY DEFINITION
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| 18 |
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| 19 | The geometry consists of a single block of a homogenous material.
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| 20 |
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| 21 | Two parameters define the geometry :
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| 22 | - the material of the box,
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| 23 | - the (full) size of the box.
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| 24 | The default is 500 m of iron.
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| 25 |
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| 26 | In addition a transverse uniform magnetic field can be applied.
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| 27 |
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| 28 | The default geometry is constructed in DetectorConstruction class,
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| 29 | but all of the above parameters can be changed interactively via
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| 30 | the commands defined in the DetectorMessenger class.
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| 31 |
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| 32 | 2- PHYSICS LIST
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| 33 |
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| 34 | The particle list is the one of novice/exampleN03.
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| 35 | The physics list contains the 'standard' electromagnetic processes,
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| 36 | and decay.
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| 37 |
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| 38 | For Gamma, only the GammaConversionToMuons has been registered.
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| 39 | Futhermore, a high production cut (1 km, which gives infinity in energy)
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| 40 | prevent any production of delta-electrons from ionization or gamma
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| 41 | from bremsstrahlung.
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| 42 | For Positrons, only the annihilation process is selected.
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| 43 |
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| 44 |
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| 45 | 3- AN EVENT : THE PRIMARY GENERATOR
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| 46 |
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| 47 | The primary kinematic consists of a single particle which hits the
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| 48 | block perpendicular to the input face. The type of the particle
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| 49 | and its energy are set in the PrimaryGeneratorAction class, and can
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| 50 | changed via the G4 build-in commands of ParticleGun class (see
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| 51 | the macros provided with this example).
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| 52 | The default is a Gamma of 100 TeV.
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| 53 |
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| 54 | In addition one can choose randomly the impact point of the incident
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| 55 | particle. The corresponding interactive command is built in
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| 56 | PrimaryGeneratorMessenger class.
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| 57 |
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| 58 | A RUN is a set of events.
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| 59 |
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| 60 |
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| 61 | 4- VISUALIZATION
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| 62 |
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| 63 | The Visualization Manager is set in the main().
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| 64 | The initialisation of the drawing is done via the command
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| 65 | > /control/execute vis.mac
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| 66 |
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| 67 | The detector has a default view which is a longitudinal view of the box.
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| 68 |
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| 69 | The tracks are drawn at the end of event, and erased at the end of run.
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| 70 | Optionaly one can choose to draw all particles, only the charged one,
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| 71 | or none. This command is defined in EventActionMessenger class.
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| 72 |
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| 73 | 5- PHYSICS DEMO
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| 74 |
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| 75 | The particle's type and the physic processes which will be available
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| 76 | in this example are set in PhysicsList class.
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| 77 |
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| 78 | In addition a build-in interactive command (/process/inactivate proname)
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| 79 | allows to activate/inactivate the processes one by one.
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| 80 |
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| 81 | The threshold for producing secondaries can be changed.
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| 82 | eg: /run/particle/setCut 100 micrometer
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| 83 | /run/initialize
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| 84 |
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| 85 | To visualize the GammaConversionToMuons :
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| 86 | /control/execute run01.mac
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| 87 | /control/execute vis.mac
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| 88 | /run/beamOn
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| 89 |
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| 90 | To visualize the AnnihiToMuPair :
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| 91 | /control/execute run11.mac
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| 92 | /control/execute vis.mac
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| 93 | /run/beamOn
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| 94 |
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| 95 | 6- HOW TO START ?
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| 96 |
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| 97 | - compile and link to generate an executable
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| 98 | % cd geant4/examples/extended/electromagnetic/TestEm6
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| 99 | % gmake
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| 100 |
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| 101 | - execute Test in 'batch' mode from macro files
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| 102 | % TestEm6 run01.mac
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| 103 |
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| 104 | - execute Test in 'interactive mode' with visualization
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| 105 | % TestEm6
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| 106 | ....
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| 107 | Idle> type your commands
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| 108 | ....
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| 109 | Idle> exit
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| 110 |
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| 111 | 7- HOW TO INCREASE STATISTICS ON gamma -> mu+mu- ?
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| 112 |
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| 113 | The processes of gamma -> mu+mu- and e+e- -> mu+mu-
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| 114 | have a low cross section but can be important
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| 115 | for leakage through thick absorbers and calorimeters.
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| 116 | Straight forward simulation will be quite time consuming.
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| 117 | To make the processes more visible, the cross section can be
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| 118 | artificially increased by some factor (here 1000)
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| 119 | using the commands (only effective after /run/initialize)
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| 120 |
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| 121 | /testem/phys/SetGammaToMuPairFac 1000
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| 122 | /testem/phys/SetAnnihiToMuPairFac 1000
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| 123 |
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| 124 |
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| 125 | 8- HISTOGRAMS
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| 126 |
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| 127 | Testem6 produces 6 histograms which illustrate the final state of
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| 128 | the GammaConversionToMuons process. See their definitions in RunAction.cc
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| 129 |
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| 130 | By default the histograms are not activated. To activate histograms
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| 131 | the environment variable G4ANALYSIS_USE should be defined. For instance
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| 132 | uncomment the flag G4ANALYSIS_USE in GNUmakefile.
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| 133 |
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| 134 | Before compilation of the example it is optimal to clean up old files:
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| 135 | gmake histclean
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| 136 | gmake
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| 137 |
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| 138 | By default the histograms are saved as testem6.root
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| 139 | It is possible to choose the format of the histogram file (hbook, root, XML):
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| 140 | comment/uncomment 1 line in the constructor of RunAction.
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| 141 |
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| 142 | To use histograms, at least one of the AIDA implementations should be
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| 143 | available. See InstallAida.txt
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