[1337] | 1 | $Id: README,v 1.17 2008/09/18 16:42:07 maire Exp $ |
---|
[807] | 2 | ------------------------------------------------------------------- |
---|
| 3 | |
---|
| 4 | ========================================================= |
---|
| 5 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP |
---|
| 6 | ========================================================= |
---|
| 7 | |
---|
| 8 | TestEm6 |
---|
| 9 | ------- |
---|
| 10 | This example is intended to test the processes of gamma conversion |
---|
| 11 | to a pair of muons and annihilation of positrons with atomic |
---|
| 12 | electrons to a pair of muons. |
---|
| 13 | To make these process more visible, the usually much more frequent |
---|
| 14 | gamma conversion to a pair of electrons and the standard positron |
---|
| 15 | processes are not selected in the physics list. |
---|
| 16 | |
---|
| 17 | 1- GEOMETRY DEFINITION |
---|
| 18 | |
---|
| 19 | The geometry consists of a single block of a homogenous material. |
---|
| 20 | |
---|
| 21 | Two parameters define the geometry : |
---|
| 22 | - the material of the box, |
---|
| 23 | - the (full) size of the box. |
---|
| 24 | The default is 500 m of iron. |
---|
| 25 | |
---|
| 26 | In addition a transverse uniform magnetic field can be applied. |
---|
| 27 | |
---|
| 28 | The default geometry is constructed in DetectorConstruction class, |
---|
| 29 | but all of the above parameters can be changed interactively via |
---|
| 30 | the commands defined in the DetectorMessenger class. |
---|
| 31 | |
---|
| 32 | 2- PHYSICS LIST |
---|
| 33 | |
---|
| 34 | The particle list is the one of novice/exampleN03. |
---|
| 35 | The physics list contains the 'standard' electromagnetic processes, |
---|
| 36 | and decay. |
---|
| 37 | |
---|
| 38 | For Gamma, only the GammaConversionToMuons has been registered. |
---|
| 39 | Futhermore, a high production cut (1 km, which gives infinity in energy) |
---|
| 40 | prevent any production of delta-electrons from ionization or gamma |
---|
| 41 | from bremsstrahlung. |
---|
| 42 | For Positrons, only the annihilation process is selected. |
---|
| 43 | |
---|
| 44 | |
---|
| 45 | 3- AN EVENT : THE PRIMARY GENERATOR |
---|
| 46 | |
---|
| 47 | The primary kinematic consists of a single particle which hits the |
---|
| 48 | block perpendicular to the input face. The type of the particle |
---|
| 49 | and its energy are set in the PrimaryGeneratorAction class, and can |
---|
| 50 | changed via the G4 build-in commands of ParticleGun class (see |
---|
| 51 | the macros provided with this example). |
---|
| 52 | The default is a Gamma of 100 TeV. |
---|
| 53 | |
---|
| 54 | In addition one can choose randomly the impact point of the incident |
---|
| 55 | particle. The corresponding interactive command is built in |
---|
| 56 | PrimaryGeneratorMessenger class. |
---|
| 57 | |
---|
| 58 | A RUN is a set of events. |
---|
| 59 | |
---|
| 60 | |
---|
| 61 | 4- VISUALIZATION |
---|
| 62 | |
---|
| 63 | The Visualization Manager is set in the main(). |
---|
| 64 | The initialisation of the drawing is done via the command |
---|
| 65 | > /control/execute vis.mac |
---|
| 66 | |
---|
| 67 | The detector has a default view which is a longitudinal view of the box. |
---|
| 68 | |
---|
| 69 | The tracks are drawn at the end of event, and erased at the end of run. |
---|
| 70 | Optionaly one can choose to draw all particles, only the charged one, |
---|
| 71 | or none. This command is defined in EventActionMessenger class. |
---|
| 72 | |
---|
| 73 | 5- PHYSICS DEMO |
---|
| 74 | |
---|
| 75 | The particle's type and the physic processes which will be available |
---|
| 76 | in this example are set in PhysicsList class. |
---|
| 77 | |
---|
| 78 | In addition a build-in interactive command (/process/inactivate proname) |
---|
| 79 | allows to activate/inactivate the processes one by one. |
---|
| 80 | |
---|
| 81 | The threshold for producing secondaries can be changed. |
---|
| 82 | eg: /run/particle/setCut 100 micrometer |
---|
| 83 | /run/initialize |
---|
| 84 | |
---|
| 85 | To visualize the GammaConversionToMuons : |
---|
| 86 | /control/execute run01.mac |
---|
| 87 | /control/execute vis.mac |
---|
| 88 | /run/beamOn |
---|
| 89 | |
---|
| 90 | To visualize the AnnihiToMuPair : |
---|
| 91 | /control/execute run11.mac |
---|
| 92 | /control/execute vis.mac |
---|
| 93 | /run/beamOn |
---|
| 94 | |
---|
| 95 | 6- HOW TO START ? |
---|
| 96 | |
---|
| 97 | - compile and link to generate an executable |
---|
| 98 | % cd geant4/examples/extended/electromagnetic/TestEm6 |
---|
| 99 | % gmake |
---|
| 100 | |
---|
| 101 | - execute Test in 'batch' mode from macro files |
---|
| 102 | % TestEm6 run01.mac |
---|
| 103 | |
---|
| 104 | - execute Test in 'interactive mode' with visualization |
---|
| 105 | % TestEm6 |
---|
| 106 | .... |
---|
| 107 | Idle> type your commands |
---|
| 108 | .... |
---|
| 109 | Idle> exit |
---|
| 110 | |
---|
| 111 | 7- HOW TO INCREASE STATISTICS ON gamma -> mu+mu- ? |
---|
| 112 | |
---|
| 113 | The processes of gamma -> mu+mu- and e+e- -> mu+mu- |
---|
| 114 | have a low cross section but can be important |
---|
| 115 | for leakage through thick absorbers and calorimeters. |
---|
| 116 | Straight forward simulation will be quite time consuming. |
---|
| 117 | To make the processes more visible, the cross section can be |
---|
| 118 | artificially increased by some factor (here 1000) |
---|
| 119 | using the commands (only effective after /run/initialize) |
---|
| 120 | |
---|
| 121 | /testem/phys/SetGammaToMuPairFac 1000 |
---|
| 122 | /testem/phys/SetAnnihiToMuPairFac 1000 |
---|
| 123 | |
---|
| 124 | |
---|
| 125 | 8- HISTOGRAMS |
---|
| 126 | |
---|
| 127 | Testem6 produces 6 histograms which illustrate the final state of |
---|
| 128 | the GammaConversionToMuons process. See their definitions in RunAction.cc |
---|
| 129 | |
---|
| 130 | By default the histograms are not activated. To activate histograms |
---|
| 131 | the environment variable G4ANALYSIS_USE should be defined. For instance |
---|
| 132 | uncomment the flag G4ANALYSIS_USE in GNUmakefile. |
---|
| 133 | |
---|
| 134 | Before compilation of the example it is optimal to clean up old files: |
---|
| 135 | gmake histclean |
---|
| 136 | gmake |
---|
| 137 | |
---|
[1337] | 138 | By default the histograms are saved as testem6.root |
---|
[807] | 139 | It is possible to choose the format of the histogram file (hbook, root, XML): |
---|
| 140 | comment/uncomment 1 line in the constructor of RunAction. |
---|
| 141 | |
---|
| 142 | To use histograms, at least one of the AIDA implementations should be |
---|
[1337] | 143 | available. See InstallAida.txt |
---|