Example Pol01

How to compute and plot the QED processes including polarization. Two possible scenarios are available:

• Polarization transfer of an incoming beam to final state particles
• Material dependent transmission of a polarized beams. The method is explained below : see item Physics.

GEOMETRY DEFINITION

The geometry consists of a single block of a homogeneous material, placed in a world.

Three parameters define the geometry :

• the material of the box,
• the thickness of the box (sizeZ),
• the transverse dimension of the box (sizeXY).

The default geometry (5mm of Iron, G4_Fe) is constructed in DetectorConstruction, but the above parameters can be changed interactively via the commands defined in DetectorMessenger. Its polarization can be accessed via the G4PolarizationMessenger (see example macro file), and is given in the global coordinate system.

PHYSICS LIST

The Physics List contains QED particle definitions (electrons, positrons and photons) and a general transportation process. In addition the user can add one of the two process modules:

• 1. "standard" - standard (unpolarized) EM physics
• 2. "polarized" - polarized EM physics

These physics list contain the standard electromagnetic processes.

AN EVENT : THE PRIMARY GENERATOR

The primary kinematic consists of a single particle starting at the edge of the box. The type of the particle and its energy are set in PrimaryGeneratorAction (10 MeV electron). By default the G4ParticleGun polarization is zero. All parameter can be changed via the G4 build-in commands of ParticleGun class (see the macros provided with this example).

PHYSICS

This example uses the following physics processes:

• electromagnetic:
  • photo-electric effect
  • Compton scattering
  • pair production
  • bremsstrahlung
  • ionization
  • multiple scattering
  • annihilation

or

• polarized electromagnetic: (incl. simulation of polarization transfer, and asymmetries for longitudinally polarized leptons, and circularly polarized photons)
  • polarized photo-electric effect
  • polarized Compton scattering
  • polarized pair production
  • polarized bremsstrahlung
  • polarized ionization
  • multiple scattering
  • polarized annihilation

and

• transportation

and defines the following particles:

electron, positron, photon

HISTOGRAMS

The test contains 12 built-in 1D histograms, which are managed by the HistoManager class and its messenger, HistoMessenger. The histos can be individually activated with the command :

/testem/histo/setHisto id nbBins  valMin valMax unit 

where unit is the desired unit for the histo (MeV or keV, etc..) (see the macro histos.mac).

• 1 gamma energy
• 2 gamma cos(theta)
• 3 gamma phi
• 4 gamma polarization
• 5 electron energy
• 6 electron cos(theta)
• 7 electron phi
• 8 electron polarization
• 9 positron energy
• 10 positron cos(theta)
• 11 positron phi
• 12 positron polarization

% gmake plots

VISUALIZATION

Simulated events can be displayed on top of a representation of the geometry, see vis.mac for an example.

HOW TO START ?

• Execute Pol01 in 'batch' mode from the default macro file :

  % Pol01   pol01.in
  

• Execute Pol01 in 'batch' mode including analysis output :

  % Pol01   histos.mac
  

• If available use JAIDA to display the results via

  % gmake plots
  

• A visualisation example is available by calling

  % Pol01  
  [...]
  PreInit> /control/execute vis.mac