Geant4 Simulations to Characterize Low-Energy Charged Particle Scattering on Flat Material Surfaces

As a recipient of an IPP Summer Student Fellowship for the summer of 2023, June through August was spent working with the Accelerator and Beam Physics Group of the Beams department at CERN in Geneva, Switzerland, as part of the CERN Summer Student Programme. The project consisted of Geant4 simulation and data analysis of low-energy charged particle scattering off of various flat material surfaces, with the goal of characterising such scattering and applying our findings to tapered capillaries for beam density enhancement and potential beam cooling. In the early 2010s, studies at the RIKEN-RAL muon facility and the TRIUMF M9B muon beamline demonstrated the use of tapered capillaries to improve muon beam density. We developed a Geant4-based code to simulate the internal reflection experienced by such particles. Analysis of these simulations revealed unique and unexpected reflection behaviour of muons, electrons, and protons in the 10MeV/c to 500MeV/c momentum range, when scattered off various different elemental, composite and coated materials. In addition, we developed a second simulation framework to test tapered capillaries of linear, polynomial, and hyperbolic profiles, with different elemental, composite, and coated materials. The analysis of this second simulation is ongoing.