BESS-polar measurements of the cosmic-ray proton and helium spectra

Abstract

The energy spectra of cosmic-ray protons and helium near solar minimum were measured with BESS-Polar (Balloon-borne Experiment with a Superconducting Spectrometer-Polar) during long-duration flights over Antarctica in December 2004 and December 2007, and are discussed here. The absolute fluxes and spectral shapes of primary protons and helium probe the origin and the propagation history of cosmic rays in the Galaxy. The spectra are also essential as inputs to calculate the spectrum of cosmic-ray antiprotons, which are secondary products of cosmic-ray interactions with the interstellar gas. We report absolute spectra at the top of the atmosphere for cosmic-ray protons in the kinetic energy range 0.2-160 GeV and helium nuclei 0.2-80 GeV/nucleon [1].