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

*Corresponding author for this work

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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