Study of the Origin of the Cosmic-Ray Antiprotons using the BESS Spectrometer

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In order to study the origin of the cosmic-ray antiprotons,1. Two successive balloon-borne experiments with the BESS superconducting spectrometer have been carried out in 1999 and 2000 to measure precise spectrum of the cosmic rays at the solar maximum period. In these flights, more than thousand antiproton events were accumulated.2. By the data from those flights, charge dependence on the solar modulation was clearly observed, which is inevitable to understand the energy spectrum of secondary antiprotons.3. A search for antihelium nuclei in the primary cosmic rays has been carried out and an upper limit of the ratio of antiheliums to helium nuclei to be less than 7×10^<-7> was placed, which is most stringent in the world.4. Precise energy spectrum of primary protons was measured, especially in low energy region below 1 GeV.Using the data during the acsend of the balloon, residual pressure dependence on the proton spectrum was observed in order to check models of the development of cosmic rays in the atmosphere.5. The 7^<th> BESS workshop was held to evaluate the results from past BESS experiments. For further investigation of the primary origin of the low energy antiprotons, a longer balloon-borne experiment with smaller superconducting spectrometer was discussed and planed by a long duration flight in Antarctica in that workshop.