First measurement of the absorption of ${}^3\overline{He}$ and ${}^3\overline{H}$ nuclei in matter and its impact on ${}^3\overline{He}$ propagation in the galaxy

Antinuclei in cosmic rays have long been considered a golden channel for indirect WIMP dark matter searches, since WIMPs are predicted to be able to annihilate to create antinuclei. They are considered such a promising probe because the expected antinuclei signal from dark matter at low kinetic energies exceeds the background expected fromother astrophysical sources by sever orders of magnitude. Indeed, only a single relevant background source is considered: the collision of high energy cosmic rays with the interstellar medium. Current generation experiments are reaching sensitivities which can probe optimistic models, and next generation experiments will be able to fully resolve any such signal, if it exists. In order to decode any information from such a signal, all effects acting on it must be understood, and the uncertainties on each of these effects must me known. The relevant processes are the production, propagation, and finally annihilation of these antinuclei. On earth, antinuclei are produced in high energy particle collisions at particle colliders. Due to their rarity, traditional fixed target experiments employed to measure the annihilation probabilities (called the inelastic cross section) of particles cannot be used for low energy antinuclei. The work presented in this thesis used a recently developed new experimental method to measure the inelastic cross sections of ${}^3\overline{He}$ and ${}^3\overline{H}$ for the first time, and used these measurements in order to infer the effect of annihilation on the expected antinuclei flux in cosmic rays. Furthermore, the same procedure for evaluating the effect of antinuclei inelastic cross sections on their propagation has been applied to antideuterons. In the course of this work, the uncertainties concerning the propagation and production of antinuclei have also been re-evaluated. The work carried out as part of my PhD has thus involved measuring the measurement of the inelastic cross sections of the A=3 antinuclei ${}^3\overline{He}$ and ${}^3\overline{H}$, aswell as using them in order to determine the experimental uncertainties on ${}^3\overline{He}$ and antideuteron fluxes due to annihilation, both for the first time.