A study of backscattering in high energy cosmic-ray experiments

In high-energy cosmic-ray instruments in space, as well as in experiments at particle accelerators, backscattered secondary particles (BSC) pose a significant challenge to tracking and to particle identification. The present thesis investigates the physical origin, characteristics and impact of BSC radiation in a conceptual test apparatus consisting of a sampling calorimeter and a charge detector (CHD), using detailed Geant4-based Monte Carlo simulations with incident proton and electron beams with energies ranging from 100 GeV to 10 TeV. A realistic detector geometry was implemented, consisting of a sampling calorimeter composed of alternating layers of lead (absorber) and plastic scintillator, preceded by a thin (300 µm ) sili- con charge detector located upstream. Primary cosmic-ray particles interact with the calorimeter, producing complex electromagnetic and hadronic showers. A fraction of secondary particles are backscattered toward the CHD, depositing energy and potentially mimicking signal events generated by the beam particles hitting the CHD. We systematically categorized all BSC particle types—photons, electrons, protons, neutrons, pions, muons, kaons, and neutral mesons—and studied their kinetic energy, angular distribution, velocity (β ), arrival time, and energy deposition profiles. To disentangle fake signals from genuine events, cuts based on deposited energy and time-of- flight were applied. The timing structure of BSC particles demonstrated a clear separation between fast (electrons, photons) and slow (neutrons, heavy particles) components. Additionally, studies of a pixelated geometry of the CHD were carried out to evaluate the rejection efficiency of low-energy BSC signals, showing that a high granularity combined with sub-nanosecond timing can suppress a significant fraction of the BSC background. This work provides an insight into the underlying physical phenomena at the basis of backscatter- ing in high-energy detectors, offering strategies for background rejection and improved detector design for future cosmic-ray experiment and space instrumentation.