Gabriele Cosmo
137 lines
4.5 KiB
Plaintext
137 lines
4.5 KiB
Plaintext
$Id: README,v 1.2 2007/12/04 10:34:17 schaelic 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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TestPolarization
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----------------
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How to compute and plot the QED processes including
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polarization.
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Two possible scenarios are available:
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- Polarization transfer of an incoming beam to final state particles
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- Material dependent transmission of a polarized beams.
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The method is explained below : see item Physics.
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1- GEOMETRY DEFINITION
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The geometry consists of a single block of a homogeneous material,
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placed in a world.
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Three parameters define the geometry :
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- the material of the box,
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- the thickness of the box (sizeZ),
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- the transverse dimension of the box (sizeXY).
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The default geometry (5mm of Iron, G4_Fe) is constructed in
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DetectorConstruction, but the above parameters can be changed
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interactively via the commands defined in DetectorMessenger.
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Its polarization can be accessed via the PolarizationMessenger
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(see example macro file), and is given in the global coordinate
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system.
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2- PHYSICS LIST
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The Physics List contains QED particle definitions (electrons,
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positrons and photons) and a general transportation process.
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In addition the user can add one of the two process modules:
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1. "standard" - standard (unpolarized) EM physics
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2. "polarized" - polarized EM physics
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These physics list contain the standard electromagnetic processes.
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3- AN EVENT : THE PRIMARY GENERATOR
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The primary kinematic consists of a single particle starting
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at the edge of the box. The type of the particle and its
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energy are set in PrimaryGeneratorAction (10 MeV electron).
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By default the ParticleGun polarization is zero.
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All parameter can be changed via the G4 build-in commands of
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ParticleGun class (see the macros provided with this example).
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4- PHYSICS
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This example uses the following physics processes:
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- electromagnetic:
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photo-electric effect
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Compton scattering
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pair production
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bremsstrahlung
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ionization
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multiple scattering
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annihilation
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or
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- polarized electromagnetic:
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(incl. simulation of polarization transfer, and
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asymmetries for longitudinally polarized leptons, and
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circularly polarized photons)
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polarized photo-electric effect
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polarized Compton scattering
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polarized pair production
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polarized bremsstrahlung
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polarized ionization
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multiple scattering
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polarized annihilation
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and
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- transportation
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and defines the following particles:
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electron, positron, photon
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5- HISTOGRAMS
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The test contains 12 built-in 1D histograms, which are managed by the
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HistoManager class and its Messenger. The histos can be individually
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activated with the command :
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/testem/histo/setHisto id nbBins valMin valMax unit
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where unit is the desired unit for the histo (MeV or keV, etc..)
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(see the macro histos.mac).
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1 gamma energy
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2 gamma cos(theta)
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3 gamma phi
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4 gamma polarization
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5 electron energy
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6 electron cos(theta)
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7 electron phi
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8 electron polarization
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9 positron energy
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10 positron cos(theta)
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11 positron phi
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12 positron polarization
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If AIDA is available, i.e. if G4ANALYSIS_USE is set, these
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histograms are stored in a compressed XML file
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(pol01.aida). These results can be displayed using a small
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program (plotResults.java) based on JAIDA by simply calling
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% gmake plots
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6- VISUALIZATION
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Simulated events can be displayed on top of a representation of
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the geometry, see vis.mac for an example.
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7- HOW TO START ?
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compile and link to generate an executable
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% gmake
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execute pol01 in 'batch' mode from the default macro file :
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% pol01 pol01.in
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or execute pol01 in 'batch' mode including aida output :
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% pol01 histos.mac
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if available use JAIDA to display the results via
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% gmake plots
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a visualisation example is available by calling
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% pol01
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[...]
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PreInit> /control/execute vis.mac
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