Gabriele Cosmo\page Examplech3 Example ch3
\author Alexei Sytov - INFN Ferrara Division (Italy) \n sytov@fe.infn.it
INTRODUCTION
Example ch3 demonstrates the minimum requirements necessary to integrate the G4CoherentPairProduction process into a project, along with the G4ChannelingFastSimModel and G4BaierKatkov models, to simulate the physics of electromagnetic showers in an oriented crystal.
The key concept is the acceleration of electromagnetic processes (both radiation and pair production) in an oriented crystal, which can significantly reduce the effective radiation length [1,2]. Potential applications include electron/positron sources for accelerator experiments, as well as crystalline oriented calorimeters for collider and space applications [1,2].
This example serves as a guideline for users on how to add this physics to their existing Geant4 projects. It includes the minimum necessary options to incorporate this physics. Specifically, it requires registering G4FastSimulationPhysics and G4CoherentPairProductionPhysics in the main routine and adding a few lines of code in DetectorConstruction.
All of this physics does not depend on the physics list. In particular, the process G4CoherentPairProduction simulates only coherent part of pair production in the crystal volume, while the incoherent one should be simulated with standard Geant4 processes.
DESCRIPTION
The example simulates high energy photon interaction (typically above 10 GeV) with an oriented W crystal with <111> crystal axes aligned along the photon beam direction.
The structure of this example is very similar to the example ch1. ch3 includes a straight W crystal and a detector positioned behind it. The incoming photon beam is set up in macro run.mac.
One can also use the Geant4 GUI by launching the code without specifying a macro file. In this case, the visualization setup is automatically loaded through the vis.mac and init_vis.mac macro files. The initial beam distribution in this setup will be identical to that in run.mac.
The example does not include any input of the model or geometry parameters from the macro to keep it as straightforward as possible. The output is recorded into the file results.root. It consists of the spectrums of e-, e+ and gamma arriving to the detector. To build these plots, one has to open this file in root and use
Spectrum_electrons->Draw()
Spectrum_positrons->Draw()
and
Spectrum_gamma->Draw()
for e-, e+ and gamma, respectively.
REFERENCES
-# V. N. Baier, V. M. Katkov, V. M. Strakhovenko. Electromagnetic Processes at High Energies in Oriented Single Crystals (World Scientific, Singapore, 1998). -# L. Bandiera, V.V. Tikhomirov et al. Phys. Rev. Lett. 121, 021603 (2018).