Anisotropy of Protons and Light Primary Nuclei in Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the ISS

Abstract

A measurement of the cosmic ray anisotropy on the arrival directions of protons and light primary 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 9 years of data taking. The results for the different particle species are consistent with isotropy and upper limits on the dipole amplitude ( ) have been computed. In particular, an upper limit of < 0.32% at the 95% C.I. is established for galactic protons above 200 GV. On the other hand, limits on the dipole anisotropy of galactic helium, carbon and oxygen above 200 GV are quoted: < 0.32%, < 1.62% and < 1.69%, respectively.

Rapporteur Talk: Cosmic Ray Direct

“…The limits are usually presented for a sample integrated in rigidity above a certain minimum value. No excess has been detected, however, and instead the upper limits are in agreement with the expectations from an isotropic distribution of arrival directions [69]. A similar conclusion can be reached for CR electrons and positrons [70].…”