# Galactic cosmic-ray model in the light of AMS-02 nuclei data

## TL;DR

This paper uses recent AMS-02 cosmic ray data to constrain models of cosmic ray sources and propagation in the Milky Way, revealing differences between proton and heavier nuclei and highlighting limitations of current models.

## Contribution

It provides a comprehensive global fit of cosmic ray data considering various propagation models, and uncovers the need for different source or propagation mechanisms for different nuclei.

## Key findings

- Data with antiproton-to-proton ratio constrains propagation parameters.
- Small convection is favored in the propagation models.
- Differences between proton and helium spectra suggest distinct sources or mechanisms.

## Abstract

Cosmic ray (CR) physics has entered a precision-driven era. With the latest AMS-02 nuclei data (boron-to-carbon ratio, proton flux, helium flux and antiproton-to-proton ratio), we perform a global fitting and constrain the primary source and propagation parameters of cosmic rays in the Milky Way by considering 3 schemes with different data sets (with and without $\bar{\mathrm{p}}/\mathrm{p}$ data) and different propagation models (diffusion-reacceleration and diffusion-reacceleration-convection models). We find that the data set with $\bar{\mathrm{p}}/\mathrm{p}$ data can remove the degeneracy between the propagation parameters effectively and it favors the model with a very small value of convection (or disfavors the model with convection). The separated injection spectrum parameters are used for proton and other nucleus species, which reveal the different breaks and slopes among them. Moreover, the helium abundance, antiproton production cross sections and solar modulation are parametrized in our global fitting. Benefited from the self-consistence of the new data set, the fitting results show a little bias, and thus the disadvantages and limitations of the existed propagation models appear. Comparing to the best fit results for the local interstellar spectra ($\phi = 0$) with the VOYAGER-1 data, we find that the primary sources or propagation mechanisms should be different between proton and helium (or other heavier nucleus species). Thus, how to explain these results properly is an interesting and challenging question.