Search for anti-matter in the universe
Prof. Dr. Peter von Ballmoos (IRAP, Toulouse, France)

The tentative detection of a few anti-Helium nuclei [1] is presently revitalising the discussion on the existence of baryonic antimatter in the Universe. As ”the discovery of a single anti-helium nucleus in the cosmic ray flux would definitely point toward the existence of stars and even of entire galaxies made of anti-matter” [2] it has been proposed that the anti-Helium nuclei could originate from anti-clouds or anti-stars in the solar vicinity [3]. We discuss possible entities of antimatter in the Universe that would be probed through ordinary matter, with annihilation-radiation providing indirect evidence for their presence [4]. The observations of high energy (∼ 100 MeV) gamma-rays sets limits on the fraction of nuclear antimatter contained in our local and Galactic neighbourhood. We review recent gamma-ray [5] observations that set upper limits on such emissions.

[1] S. Ting, https://indico.cern.ch/event/729900, (2018)
[2] P.Salati, et al., Nuclear Physics B, 70, 1-3, 492, (1999)
[3] V. Poulin, et al., Phs. Rev. D 99, 023016, (2019)
[4] P. von Ballmoos, Hyperfine Interact. 228, 91,, (2014)
[5] S. Dupourque, et al., Phs. Rev. D 103, 083016, (2021)