T. Sanuki

Precision Measurement of Cosmic-Ray Antiproton Spectrum

The energy spectrum of cosmic-ray antiprotons ( &pmacr;s) has been measured in the range 0.18-3.56 GeV, based on 458 &pmacr;s collected by BESS in a recent solar-minimum period. We have detected for the first time a characteristic peak at 2 GeV of &pmacr;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 &pmacr; components.

Successive measurements of cosmic-ray antiproton spectrum in a positive phase of the solar cycle

Abstract The energy spectrum of cosmic-ray antiprotons ( p s) has been measured by BESS successively in 1993, 1995, 1997 and 1998. In total, 848 p s were clearly identified in energy range 0.18–4.20 GeV. From these successive measurements of the p spectrum at various solar activity, we discuss about the effect of the solar modulation and the origin of cosmic-ray p s. The p / p ratios showed no distinctive year-to-year variation during the positive Suns polarity phase.