The energy spectrum of cosmic-ray antiprotons ( $\overline{p}$'s) has been measured in the range 0.18–3.56 GeV, based on 458 $\overline{p}$'s collected by BESS in a recent solar-minimum period. We have detected for the first time a characteristic peak at 2 GeV of $\overline{p}$'s originating from cosmic-ray interactions with the interstellar gas. The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation. Future BESS data with still higher statistics will allow us to study the solar modulation and the propagation in detail and to search for primary $\overline{p}$ components.

• Received 28 June 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.1078