No abstract

A precision measurement by the Alpha Magnetic Spectrometer on the International Space Station of the positron fraction in primary cosmic rays in the energy range from 0.5 to 350 GeV based on 6.8×106 positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to ∼250  GeV, but, from 20 to 250 GeV, the slope decreases by an order of magnitude. The positron fraction spectrum shows no fine structure, and the positron to electron ratio shows no observable anisotropy. Together, these features show the existence of new physical phenomena

Cosmic-ray nuclei Ñuxes are expected to be measured with high precision in the near future. For instance, high-quality data on the antiproton component could give important clues about the nature of the astronomical dark matter. A very good understanding of the di †erent aspects of cosmic-ray propagation is therefore necessary. In this paper, we use cosmic-ray nuclei data to give constraints on the di †u-sion parameters. Propagation is studied with semianalytical solutions of a di †usion model, and we give new analytical solutions for radioactively produced species. Our model includes convection and reacceleration, as well as the standard energy losses. We perform a s2 analysis over B/C data for a large number of conÐgurations obtained by varying the relevant parameters of the di †usion model. A very good agreement with B/C data arises for a number of conÐgurations, all of which are compatible with sub-Fe/Fe data. Di †erent source spectra Q(E) and di †usion coefficients K(E) have been tried, but for both parameters only one form gives a good Ðt. Another important result is that models without convection or without reacceleration are excluded. We Ðnd that the various parameters, i.e., the di †usion coefficient normalization and spectral index d, the halo thickness L , the velocity and the K 0 Alfven V A , convection velocity are strongly correlated. We obtain limits on the spectral index d of the di †usion V c coefficient, and in particular we exclude a Kolmogorov spectrum (d \ 13 ).