Towards Understanding the Origin of Cosmic-Ray Positrons

Abstract

Precision measurements of cosmic ray positrons by the Alpha Magnetic Spectrometer on the International Space Station are presented up to 1 TeV based on 1.9 million positrons. The positron flux exhibits a significant excess starting from 25.2 ±1.8 GeV followed by a sharp drop-off above 284+91-64 GeV. In the entire energy range the positron flux is well described by the sum of a diffuse term associated with low energy secondary positrons produced in the collision of cosmic rays, and a new source term of high energy positrons with a finite energy cutoff. The finite cutoff energy of the source term, Es, is established with a significance of more than 4σ, and it's value is determined to be Es = 810+310-180 GeV. These experimental data on cosmic ray positrons show that, at high energies, they predominantly originate either from dark matter collisions or from new astrophysical sources.