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1 -------------------------------------------------------------------
2
3 =========================================================
4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
5 =========================================================
6
7 Example ch3
8 -----------
9 A. Sytov
10 INFN Ferrara Division, sytov@fe.infn.it
11
12 INTRODUCTION
13 Example ch3 demonstrates the minimum requirements necessary to integrate the
14 G4CoherentPairProduction process into a project, along with the G4ChannelingFastSimModel
15 and G4BaierKatkov models, to simulate the physics of electromagnetic showers in
16 an oriented crystal.
17
18 The key concept is the acceleration of electromagnetic processes (both radiation and
19 pair production) in an oriented crystal, which can significantly reduce the effective
20 radiation length [1,2]. Potential applications include electron/positron sources for
21 accelerator experiments, as well as crystalline oriented calorimeters for collider and
22 space applications [1,2].
23
24 This example serves as a guideline for users on how to add this physics
25 to their existing Geant4 projects. It includes the minimum necessary options
26 to incorporate this physics. Specifically, it requires registering
27 G4FastSimulationPhysics and G4CoherentPairProductionPhysics in the main routine and
28 adding a few lines of code in DetectorConstruction.
29
30 All of this physics does not depend on the physics list. In particular, the
31 process G4CoherentPairProduction simulates only coherent part of pair production in
32 the crystal volume, while the incoherent one should be simulated with
33 standard Geant4 processes.
34
35 DESCRIPTION
36
37 The example simulates high energy photon interaction (typically above 10 GeV) with
38 an oriented W crystal with <111> crystal axes aligned along the photon beam direction.
39
40 The structure of this example is very similar to the example ch1.
41 ch3 includes a straight W crystal and a detector positioned behind it.
42 The incoming photon beam is set up in macro run.mac.
43
44 One can also use the Geant4 GUI by launching the code without specifying a macro file.
45 In this case, the visualization setup is automatically loaded through the vis.mac and
46 init_vis.mac macro files. The initial beam distribution in this setup will be identical
47 to that in run.mac.
48
49 The example does not include any input of the model or geometry parameters
50 from the macro to keep it as straightforward as possible. The output is recorded
51 into the file results.root. It consists of the spectrums of e-, e+
52 and gamma arriving to the detector. To build these plots, one has to
53 open this file in root and use Spectrum_electrons->Draw(), Spectrum_positrons->Draw()
54 and Spectrum_gamma->Draw() for e-, e+ and gamma, respectively.
55
56 REFERENCES
57 [1] V. N. Baier, V. M. Katkov, V. M. Strakhovenko, Electromagnetic Processes
58 at High Energies in Oriented Single Crystals (World Scientific, Singapore, 1998).
59 [2] L. Bandiera, V.V. Tikhomirov et al. Phys. Rev. Lett. 121, 021603 (2018).
