Secondary cosmic-ray nucleus spectra disfavor particle transport in the Galaxy without reacceleration

TL;DR

This study uses recent cosmic ray measurements to compare propagation models, finding that reacceleration models better explain the observed spectra and spectral hardenings without needing additional assumptions.

Contribution

It demonstrates that reacceleration models naturally account for spectral hardenings in cosmic rays, challenging models without reacceleration.

Findings

Reacceleration models fit the data significantly better than convection models.

Spectral hardenings are explained by injection hardening in reacceleration models.

Secondary-to-primary ratios are steeper at low energies in reacceleration models.

Abstract

The precise observations of Galactic cosmic ray fluxes of the secondary family, such as Li, Be, B, are expected to have significant implications on our understanding of the cosmic ray origin and propagation. Here we employ the recent very precise measurements of those species by the Alpha Magnetic Spectrometer on the International Space Station, together with their parent species (C and O), as well as the data collected by the Voyager-1 spacecraft outside the heliosphere and the Advanced Composition Explorer, to investigate the propagation of cosmic rays in the Milky Way. We consider the diffusion of cosmic rays plus reacceleration or convection effect during the propagation, and find that the reacceleration model can fit the data significantly better than the convection model. We further find that for the reacceleration model, the spectral hardenings of both the primary and secondary particles can be well described by the injection hardening without including additional propagation hardening. This is due to that the reacceleration effect results in a steeper secondary-to-primary ratio at low energies, and can thus naturally reproduce the fact that the secondary spectra harden more than the primary spectra found by AMS-02.