| Geant4 Cross Reference |
1 ------------------------------------------------------------------- 2 3 ========================================================= 4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP 5 ========================================================= 6 7 TestPolarization 8 ---------------- 9 10 How to compute and plot the QED processes including 11 polarization. 12 Two possible scenarios are available: 13 - Polarization transfer of an incoming beam to final state particles 14 - Material dependent transmission of a polarized beams. 15 The method is explained below : see item Physics. 16 17 1- GEOMETRY DEFINITION 18 19 The geometry consists of a single block of a homogeneous material, 20 placed in a world. 21 22 Three parameters define the geometry : 23 - the material of the box, 24 - the thickness of the box (sizeZ), 25 - the transverse dimension of the box (sizeXY). 26 27 The default geometry (5mm of Iron, G4_Fe) is constructed in 28 DetectorConstruction, but the above parameters can be changed 29 interactively via the commands defined in DetectorMessenger. 30 Its polarization can be accessed via the PolarizationMessenger 31 (see example macro file), and is given in the global coordinate 32 system. 33 34 2- PHYSICS LIST 35 36 The Physics List contains QED particle definitions (electrons, 37 positrons and photons) and a general transportation process. 38 In addition the user can add one of the two process modules: 39 1. "standard" - standard (unpolarized) EM physics 40 2. "polarized" - polarized EM physics 41 These physics list contain the standard electromagnetic processes. 42 43 3- AN EVENT : THE PRIMARY GENERATOR 44 45 The primary kinematic consists of a single particle starting 46 at the edge of the box. The type of the particle and its 47 energy are set in PrimaryGeneratorAction (10 MeV electron). 48 By default the ParticleGun polarization is zero. 49 All parameter can be changed via the G4 build-in commands of 50 ParticleGun class (see the macros provided with this example). 51 52 4- PHYSICS 53 54 This example uses the following physics processes: 55 56 - electromagnetic: 57 photo-electric effect 58 Compton scattering 59 pair production 60 bremsstrahlung 61 ionization 62 multiple scattering 63 annihilation 64 or 65 - polarized electromagnetic: 66 (incl. simulation of polarization transfer, and 67 asymmetries for longitudinally polarized leptons, and 68 circularly polarized photons) 69 70 polarized photo-electric effect 71 polarized Compton scattering 72 polarized pair production 73 polarized bremsstrahlung 74 polarized ionization 75 multiple scattering 76 polarized annihilation 77 and 78 - transportation 79 80 and defines the following particles: 81 electron, positron, photon 82 83 84 5- HISTOGRAMS 85 86 The test contains 12 built-in 1D histograms, which are managed by the 87 HistoManager class and its Messenger. The histos can be individually 88 activated with the command : 89 /analysis/h1/set id nbBins valMin valMax unit 90 where unit is the desired unit for the histo (MeV or keV, etc..) 91 (see the macro histos.mac). 92 93 1 gamma energy 94 2 gamma cos(theta) 95 3 gamma phi 96 4 gamma polarization 97 5 electron energy 98 6 electron cos(theta) 99 7 electron phi 100 8 electron polarization 101 9 positron energy 102 10 positron cos(theta) 103 11 positron phi 104 12 positron polarization 105 106 6- VISUALIZATION 107 108 Simulated events can be displayed on top of a representation of 109 the geometry, see vis.mac for an example. 110 111 7- HOW TO START ? 112 113 compile and link to generate an executable 114 % gmake 115 116 execute Pol01 in 'batch' mode from the default macro file : 117 % Pol01 pol01.in 118 119 or execute Pol01 in 'batch' mode including analysis output : 120 % Pol01 histos.mac 121 122 if available use JAIDA to display the results via 123 % gmake plots 124 125 a visualisation example is available by calling 126 % Pol01 127 [...] 128 PreInit> /control/execute vis.mac