# Propagation of cosmic rays in the AMS-02 era

## TL;DR

This study uses recent cosmic ray data from AMS-02 and PAMELA to constrain propagation models, finding that models with reacceleration best fit the data but reveal differences in propagation for nuclei and leptons.

## Contribution

It introduces a comprehensive comparison of propagation models using new cosmic ray data, highlighting the importance of reacceleration in fitting proton and B/C observations.

## Key findings

- Reacceleration models fit proton and B/C data well.
- Diffusion-reacceleration models predict too many low-energy positrons.
- Non-reacceleration models better fit low-energy antiproton fluxes.

## Abstract

In this work we use the newly reported Boron-to-Carbon ratio (B/C) from AMS-02 and the time-dependent proton fluxes from PAMELA and AMS-02 to constrain the source and propagation parameters of cosmic rays in the Milky Way. A linear correlation of the solar modulation parameter with solar activities is assumed to account for the time-varying cosmic ray fluxes. A comprehensive set of propagation models, with/without reacceleration or convection, have been discussed and compared. We find that only the models with reacceleration can self-consistently fit both the proton and B/C data. The rigidity dependence slope of the diffusion coefficient, $\delta$, is found to be about $0.38-0.50$ for the diffusion-reacceleration models. The plain diffusion and diffusion-convection models fit the data poorly. We compare different model predictions of the positron and antiproton fluxes with the data. We find that the diffusion-reacceleration models over-produce low energy positrons, while non-reacceleration models give better fit to the data. As for antiprotons, reacceleration models tend to under-predict low energy antiproton fluxes, unless a phenomenological modification of the velocity-dependence of the diffusion coefficient is applied. Our results suggest that there could be important differences of the propagation for nuclei and leptons, in either the Milky Way or the solar heliosphere.