Anisotropy of Cosmic Ray Fluxes Measured with the Alpha Magnetic Spectrometer on the ISS

TL;DR

This study measures the anisotropy in cosmic ray fluxes using AMS data from the ISS, finding results consistent with isotropy and setting upper limits on anisotropy amplitudes across various particle species and energies.

Contribution

First comprehensive anisotropy measurements for multiple cosmic ray species using AMS data over several years, establishing upper limits on anisotropy amplitudes.

Findings

Cosmic ray fluxes are consistent with isotropy within measurement limits.

Upper limits on dipole anisotropy are set for different particles and energies.

No significant anisotropy detected in the measured data.

Abstract

A measurement of the dipole anisotropy in galactic coordinates for different charged cosmic rays has been performed with the Alpha Magnetic Spectrometer (AMS) onboard the International Space Station (ISS). Results are presented for the first 7.5 years of data taking for protons, Helium, Carbon and Oxygen, and 6.5 years for positrons and electrons. All the species are found to be consistent with isotropy and upper limits to the dipole amplitude have been computed. In particular, for energies above 16 GeV a limit of delta < 1.9% and delta < 0.5% at the 95% C.I. is found for positrons and electrons respectively. For rigidities above 200 GV a limit of delta < 0.38%, delta < 0.36%, delta < 1.9% and delta < 1.7% is obtained for protons, Helium, Carbon and Oxygen.