Cosmic Rays belowZ = 30 in a Diffusion Model: New Constraints on Propagation Parameters

Abstract

Cosmic-ray nuclei fluxes 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 different aspects of cosmic-ray propagation is therefore necessary. In this paper, we use cosmic-ray nuclei data to give constraints on the diffusion parameters. Propagation is studied with semianalytical solutions of a diffusion 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 χ² analysis over B/C data for a large number of configurations obtained by varying the relevant parameters of the diffusion model. A very good agreement with B/C data arises for a number of configurations, all of which are compatible with sub-Fe/Fe data. Different source spectra Q(E) and diffusion coefficients K(E) have been tried, but for both parameters only one form gives a good fit. Another important result is that models without convection or without reacceleration are excluded. We find that the various parameters, i.e., the diffusion coefficient normalization K₀ and spectral index δ, the halo thickness L, the Alfvén velocity V_A, and the convection velocity V_c are strongly correlated. We obtain limits on the spectral index δ of the diffusion coefficient, and in particular we exclude a Kolmogorov spectrum (δ = ).