Search for cosmic-ray antiparticles of primary origins by ballooning a superconducting spectrometer in Antarctica

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The BESS-Polar experiment has been carried out to investigate elementary particle phenomena in early Universe through a precise measurement of low-energy antiprotons spectrum and search for antimatter in cosmic-ray with a long duration balloon flight over Antarctica. The experiment has been carried out in cooperation of KEK, Univ. Tokyo, Kobe Univ., ISAS, NASA-GSFC, Univ. Maryland, and Denver Univ.In JYF 2005, the spectrometer performance was confirmed with accelerator beam test, and further data analysis was carried out. The analysis needed to be extended in JFY2006 in order to improve the analysis and to finalize the results. Finally, we have detected more than 1500 antiproton flux in the energy region 0.1-4.2 GeV with the long duration flight in Antarctica.The energy spectrum generally agreed with the theoretical model for the secondary product in cosmic-rays. It is reasonably understood, based on the observation period of a transient period of the solar activity transient to the coming solar minimum period.The result gives us a basic understanding the antiproton spectrum in the transient period to be compared with the measurement to be carried out in the next solar minimum period in 2007. The further investigation will become very much important.