Search for cosmic-ray antideuterons with BESS-Polar

Although cosmic-ray antideuterons can be produced in primary cosmic-ray interactions with the interstellar medium in the same way as cosmic-ray antiprotons, the probability is much smaller, especially at low energies, because of the very low production cross-section and strict kinematic requirement compared to secondary antiproton production. The lack of significant astrophysical background indicates that a search for low-energy antideuterons could be a good probe for a novel production mechanisms such as pair-annihilation of neutralino dark matter or evaporation of primordial black holes. The BESS-Polar program has accumulated cosmic-ray data in near solar minimum conditions with more than ten times the statistics of those obtained by BESS flights during the previous solar minimum period. Based on these data, we perform a new antideuteron search with unprecedented sensitivity.