Abstract
A measurement of the cosmic ray anisotropy on the arrival directions of elementary particles (electrons, positrons and protons) and light nuclei (helium, carbon and oxygen) has been performed in galactic coordinates by the Alpha Magnetic Spectrometer onboard the International Space Station. The analysis is based on the sample of events collected in the first 6.5 years (electrons and positrons), and 7.5 (protons, helium, carbon and oxygen) of data taking. The results are consistent with isotropy for all cosmic ray species and upper limits on the dipole amplitude have been computed. In particular, 95% credible interval upper limits of δ < 1.9% and δ < 0.5% are obtained for positrons and electrons, respectively, above 16 GeV. On the other hand, the upper limits of protons, helium, carbon and oxygen above 200 GV are found to be δ < 0.38%, δ < 0.36%, δ < 1.9% and δ < 1.7%, respectively.
Highlights
In the last years, the Alpha Magnetic Spectrometer (AMS-02) onboard the International Space Station (ISS) has provided precise measurements of cosmic ray fluxes, which have revealed many unexpected features that cannot be fully explained within the current understanding of cosmic rays acceleration and propagation.On the one hand, the positron spectrum [1] shows a significant excess above ∼25 GeV followed by a sharp dropoff above ∼284 GeV with a finite exponential energy cutoff at ∼810 GeV established at more than 4σ
A measurement of the cosmic ray anisotropy on the arrival directions of elementary particles and light nuclei has been performed in galactic coordinates by the Alpha Magnetic Spectrometer onboard the International Space Station
The electron spectrum [4] exhibits a significant excess above ∼42 GeV compared to the lower energy trends, which is well described by the sum of two power law contributions in the entire energy range
Summary
The Alpha Magnetic Spectrometer (AMS-02) onboard the International Space Station (ISS) has provided precise measurements of cosmic ray fluxes, which have revealed many unexpected features that cannot be fully explained within the current understanding of cosmic rays acceleration and propagation. The positron spectrum [1] shows a significant excess above ∼25 GeV followed by a sharp dropoff above ∼284 GeV with a finite exponential energy cutoff at ∼810 GeV established at more than 4σ. The observation is not consistent with a pure secondary origin of cosmic ray positrons and, in many models, the inclusion of a source term, either from dark matter annihilation or astrophysical sources [2, 3], is required to explain the origin of the excess. The electron spectrum [4] exhibits a significant excess above ∼42 GeV compared to the lower energy trends, which is well described by the sum of two power law contributions in the entire energy range.
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