Successive Measurements of Cosmic-Ray Antiproton Spectrum in a Positive   Phase of the Solar Cycle
  The energy spectrum of cosmic-ray antiprotons has been measured by BESS successively in 1993, 1995, 1997 and 1998. In total, 848 antiprotons were clearly identified in energy range 0.18 to 4.20 GeV. From these successive measurements of the antiproton spectrum at various solar activity, we discuss about the effect of the solar modulation and the origin of cosmic-ray antiprotons. Measured antiproton ratios were nearly identical during this period, and were consistent with a prediction taking the charge dependent solar modulation into account. 
T. Maeno, S. Orito, H. Matsunaga, et al, BESS Collaboration