Precise measurements of cosmic-ray antiproton spectrum in a positive phase of the solar cycle Original Research Article

The BESS spectrometer has measured the energy spectrum of cosmic-ray antiprotons successively in 1993, 1995, 1997 and 1998. In total, 848 antiprotons were clearly identified in energy range 0.18 to 4.20 GeV based on magnetic-rigidity, time-of-flight, energy loss, and Cherenkov radiation measurements. The measured antiproton spectra and antiproton/proton ratios were nearly identical at the upper end of the instrumental energy range, which is consistent with theoretical calculations. In the low energy region, our data show variations that are somewhat larger than expected. This might be due to statistical fluctuation, or might suggest a contribution of primary antiprotons from novel sources.