PAMELA Measurements of Cosmic-ray Proton and Helium Spectra

TL;DR

This paper presents precise measurements of cosmic-ray proton and helium spectra by PAMELA, revealing spectral differences that challenge existing models of cosmic-ray acceleration and propagation in the Galaxy.

Contribution

First detailed spectral measurements of cosmic-ray protons and helium nuclei over a wide energy range, showing deviations from simple power-law models.

Findings

Spectral shapes differ between protons and helium.

Data cannot be explained by a single power law.

Results challenge current cosmic-ray acceleration models.

Abstract

Protons and helium nuclei are the most abundant components of the cosmic radiation. Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in the Galaxy. We report precision measurements of the proton and helium spectra in the rigidity range 1 GV-1.2 TV performed by the satellite-borne experiment PAMELA. We find that the spectral shapes of these two species are different and cannot be well described by a single power law. These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy. More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data.