OPTIMUM RIGIDITY RANGE FOR THE COSMIC ANTIHELIUM QUEST

No cosmic antinucleus has yet been detected in the primary cosmic radi ation. Only upper limits to the antinucleus fluxes have been measured in various rigidity ranges in different experiments. Calculations of t he flux reduction experienced by cosmic antihelium traversing the Milk y Way are reported. A significant depression of the antihelium flux ha s been found in the low-momentum band 2-6 GeV/c compared to that postu lated to exist in the intergalactic space. The relevant results presen ted here are based on simple observational data regarding the total ma tter column swept by cosmic rays in the Milky Way and the expected pro perties of antihelium interactions with the interstellar hydrogen. The calculations have been made by the simulation code LEASA (Low Energy Antinucleus Simulation Algorithms) developed to describe antinucleus i nteractions with matter. Important implications of these results on pa st and future experiments giving upper limits on antihelium-to-helium flux ratios are discussed.