# Proton and Helium Spectra from the CREAM-III Flight

## TL;DR

The CREAM-III balloon experiment measured cosmic-ray proton and helium spectra above 1 TeV, finding they are harder than previous measurements at lower energies, with spectra softening above 20 TeV, though uncertainties remain.

## Contribution

First precise measurement of cosmic-ray proton and helium spectra above 1 TeV with high charge resolution from the CREAM-III balloon flight.

## Key findings

- Proton and helium spectra are harder than previous measurements at tens of GeV.
- The proton to helium ratio is about 9.53 in the TeV/n range.
- Spectra soften above approximately 20 TeV, but data uncertainties are large.

## Abstract

Primary cosmic-ray elemental spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass (CREAM) experiment since 2004. The third CREAM payload (CREAM-III) flew for 29 days during the 2007-2008 Antarctic season. Energies of incident particles above 1 TeV are measured with a calorimeter. Individual elements are clearly separated with a charge resolution of ~0.12 e (in charge units) and ~0.14 e for protons and helium nuclei, respectively, using two layers of silicon charge detectors. The measured proton and helium energy spectra at the top of the atmosphere are harder than other existing measurements at a few tens of GeV. The relative abundance of protons to helium nuclei is 9.53+-0.03 for the range of 1 TeV/n to 63 TeV/n. The ratio is considerably smaller than other measurements at a few tens of GeV/n. The spectra become softer above ~20 TeV. However, our statistical uncertainties are large at these energies and more data are needed.