Monte-Carlo Simulation of a High-Energy Electron Beam in an Optical Fibre with Geant4

The main aim of this project was to simulate a beam of high-energy electrons entering an optical fibre made from Silicone Dioxide (quartz) using Geant4. The first step was to connect to the ATLAS computing environment - this was done by using my laptop’s terminal in order to access lxplus. Once accessed, it was then possible to create and store folders on my drive remotely. A template code, obtained on CERN’s GitLab page, had a skeleton code for simulating optical fibres in Geant4. This repository was cloned using lxplus for modifications. Using Sublime through this command: source tunnel lxplus.sh, it was possible to edit the code through a ’tunnel’. The results showed the initial success of the creation of the quartz optical fibre, as well as the creation of an electron beam using Geant4. The SiO2 fibre had diameter 1.7 mm and was created in two classes: WLSMaterials and WLSDetectorConstruction where it replaced a pre-existing fibre material. The final step was to create a beam of electrons. The electron beam was created by modifying the main macro folder wls.in. The successful run of the simulation using the command ./wls in batch mode ensured that the beam had been correctly added. This was done by defining an electron beam (this goes by -e in GeneralParticleSource), whilst also defining the energy and the shape of the beam, which was successfully implemented. In order to obtain a greater understanding of the effects of a high-energy electron beam passing through the optical fibre, the next step would be to implement a code to determine events in the output file that cross a certain energy threshold, which would subsequently be the energy at which Cherenkov light would be produced. This could be done by creating a statement in the WLSEventAction.cc class, so that information printed is only for events above a certain energy. The learning objective of this project was to gain a better understanding of high-energy simulation Physics using Geant4. With only little experience working with Geant4 prior to this project, I felt that I have learned a lot more about working with lxplus and with C++.