Measurements of cosmic-ray proton and helium spectra from the BESS-Polar long-duration balloon flights over Antarctica

TL;DR

This paper presents detailed measurements of cosmic-ray proton and helium spectra from the BESS-Polar flights over Antarctica, providing valuable data for understanding cosmic-ray origins and propagation.

Contribution

It provides the first absolute spectra of cosmic-ray protons and helium over a wide energy range during two different solar modulation conditions.

Findings

Proton spectra range from 0.2 to 160 GeV

Helium spectra range from 0.15 to 80 GeV/nucleon

Proton-to-helium flux ratio analyzed from 1.1 GV to 160 GV

Abstract

The BESS-Polar Collaboration measured the energy spectra of cosmic-ray protons and helium during two long-duration balloon flights over Antarctica in December 2004 and December 2007, at substantially different levels of solar modulation. Proton and helium spectra probe the origin and propagation history of cosmic rays in the galaxy, and are essential to calculations of the expected spectra of cosmic-ray antiprotons, positrons, and electrons from interactions of primary cosmic-ray nuclei with the interstellar gas, and to calculations of atmospheric muons and neutrinos. 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 0.15-80 GeV/nucleon. The corresponding magnetic rigidity ranges are 0.6-160 GV for protons and 1.1-160 GV for helium. These spectra are compared to measurements from previous BESS flights and from ATIC-2, PAMELA, and AMS-02. We also report the ratio of the proton and helium fluxes from 1.1 GV to 160 GV and compare to ratios from PAMELA and AMS-02.