Precise Measurement of Cosmic-Ray Proton and Helium Spectra with the   BESS Spectrometer
  We report cosmic-ray proton and helium spectra in energy ranges of 1 to 120 GeV and 1 to 54 GeV/nucleon, respectively, measured by a balloon flight of the BESS spectrometer in 1998. The magnetic-rigidity of the cosmic-rays was reliably determined by highly precise measurement of the circular track in a uniform solenoidal magnetic field of 1 Tesla. Those spectra were determined within overall uncertainties of +-5 % for protons and +- 10 % for helium nuclei including statistical and systematic errors. 
T. Sanuki, M. Motoki, H. Matsumoto, E. S. Seo, J. Z. Wang, K. Abe, K.   Anraku, Y. Asaoka, M. Fujikawa, M. Imori, T. Maeno, ...