Precise measurements of the cosmic ray antiproton spectrum with BESS including the effects of solar modulation

J. W. Mitchell, K. Abe, K. Anraku, Y. Asaoka, M. Fujikawa, H. Fuke, S. Haino, T. Hams, N. Ikeda, M. Imori, A. Itazaki, K. Izumi, M. H. Lee, T. Maeno, Y. Makida, S. Matsuda, N. Matsui, T. Matsukawa, H. Matsumoto, H. MatsunagaT. Mitsui, A. Moiseev, M. Motoki, J. Nishimura, M. Nozaki, H. Omiya, S. Orito, J. F. Ormes, T. Saeki, T. Sanuki, M. Sasaki, E. S. Seo, Y. Shikaze, T. Sonoda, S. A. Stephens, R. E. Streitmatter, J. Suzuki, Y. Takasugi, K. Tanaka, K. Tanizaki, I. Ueda, J. Z. Wang, Y. Yajima, T. Yamagami, A. Yamamoto, Y. Yamamoto, K. Yamato, T. Yoshida, K. Yoshimura

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


The Balloon Borne Experiment with a Superconducting Spectrometer (BESS) has measured the energy spectrum of cosmic-ray antiprotons between 0.18 and 4.20 GeV in eight flights between 1993 and 2002. Above about 1 GeV, models in which antiprotons are secondary products of the interactions of primary cosmic rays with the interstellar gas agree with the BESS antiproton spectrum. Below 1 GeV, the data show a possible excess antiproton flux compared to secondary model predictions, suggesting the presence of an additional source of antiprotons. The antiproton/proton ratios measured between 1993 and 1999, during the Sun's positive-polarity phase, are consistent with simple models of solar modulation. However, results from the 2000 flight, following the solar magnetic field reversal, show a sudden increase in the antiproton/proton ratio and tend to favor a charge-sign-dependent drift model. To extend BESS measurements to lower energies, an evolutionary instrument, BESS-Polar, is under construction for polar flight in 2004.

Original languageEnglish
Pages (from-to)135-141
Number of pages7
JournalAdvances in Space Research
Issue number1
Publication statusPublished - 2005
Externally publishedYes


  • BESS
  • Cosmic ray antiproton spectrum
  • Solar modulation effects

ASJC Scopus subject areas

  • Aerospace Engineering
  • Astronomy and Astrophysics
  • Geophysics
  • Atmospheric Science
  • Space and Planetary Science
  • General Earth and Planetary Sciences


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