Towards a cosmic-ray and atmospheric deuteron search with the GAPS experiment

Abstract

The primary purpose of the balloon-borne General Anti-Particle Spectrometer (GAPS) experiment is to conduct a low-energy ($<$0.25 GeV/$n$) cosmic antinuclei search, optimized for the detection of antideuterons in particular. GAPS seeks to shed light on the potential particle nature of dark matter via indirect detection of these light cosmic-ray antiparticles, which are expected to be produced in dark matter annihilations or decays. This thesis focuses on deuterons for a number of reasons detailed as follows. Deuterons have high statistics relative to cosmic antinuclei and are essential to study GAPS detector effects. To claim an understanding of the complex GAPS reconstruction and identification, it is crucial to perform a deuteron analysis in conjunction with its primary proton background. There are a few reasons for this. A primary reason is because matter particles, such as deuterons, allow for the study of charged-particle energy depositions in the absence of annihilation phenomena. Therefore, a study of these particles will critically inform antideuteron identification, which is essential for the GAPS experiment’s primary mission as a low-energy antinuclei search. Deuterons and their background protons also provide a measurement for single-particle trigger events. In addition, in the GAPS energy range, the great majority of deuterons seen at the GAPS flight altitude will be atmospheric in origin. This provides an opportunity to quantify atmospheric effects for all GAPS measurements, and also to perform an atmospheric deuteron study based on its own merit. Therefore, a simulation-based study was performed for the deuteron analysis for the GAPS experiment. In addition, the process and results of the GAPS detector mass calibration effort, co-led by the author, is expounded upon. The primary goal of the calibration effort is to quantify the relative quality of the GAPS detector modules. This is accomplished via the use of an X-ray source with energies on the order of the exotic atom transition X-rays for antiparticles that are central to the GAPS technique. The successful results of this calibration effort are presented.