Towards Understanding the Origin of Cosmic-Ray Positrons

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 $25.2 \pm 1.8$ 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 termassociated 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, $E_s$, is established with a significance of more than $4 \sigma$, and it's value is determined to be $E_s = 810^{+310}_{-180}$ 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.