Geant4 simulations of monochromatic Cherenkov radiation in thin quartz targets for different experimental conditions

Abstract

In light of our recent research, we discussed the possibility of observing quasimonochromatic Cherenkov Radiation (ChR) spectral lines from a dispersive medium (thin quartz radiator). Such experimental results were verified on the Mainz Microtron MAMI, Germany [1], while both the polarization currents analytical model [2] and Geant4 [3] simulations were used to analyze the results. To describe the Cherenkov radiation process, the Geant4 toolkit uses only the approximation obtainable for an infinitely thick emitter (cos θ = 1 / βn(λ), where θ is Cherenkov’s angle of emission, β is reduced velocity, and n(λ) is a refractive index as a function of emitted radiation’s wavelength λ) and doesn’t consider its actual dimensions. Tamm’s theory [4] predicts some broadening of the ChR angular distribution with a radiator thinning. Consequently, Geant4 gave inadequate results for the pencil-like electron beams compared to the polarization currents model and the experiment. However, unlike in the analytical calculations, we needed to consider more realistic Gaussian electron beams to obtain better results with Geant4. Therefore, obtained results primarily manifest beam characteristics rather than the ChR itself, i.e., its intrinsic characteristics are masked. Now, the idea is to present additional simulation results with further variations of the quartz’s thickness (in preparation for future experiments), confirming the last conclusion without any doubt.