Cosmic-ray antiprotons and antinuclei Original Research Article

Recent progress in experimental observations and theoretical investigations of cosmic-ray antiprotons (pʹs) have brought new light on their origin. The p energy spectrum measured by the recent BESS experiment shows the characteristic peak around 2 GeV, which was expected from “secondary” pʹs, i.e., produced in cosmic-ray interactions with the interstellar gas. The MASS and CAPRICE experiments have detected pʹs in the higher energy range and show that the flux decreases beyond the peak. These new data are well reproduced by theoretical calculations recently developed. Further sensitive observations with still higher statistics are required to investigate the propagation and solar modulation models in detail and to search for the primary p component from novel sources, e.g. evaporating black holes or annihilating neutralino dark matter. In the case of antinuclei searches, an upper limit of a level of 10−6 is obtained for the antihelium/helium ratio both from the BESS balloon flight and the AMS space mission. In the future, BESS-polar and AMS on the ISS (International Space Station) may be expected to reach upper limits of 10−7 and 10−8, respectively.