Cosmic ray propagation after AMS-02
Q. Yuan, S.J. Lin, K. Fang, X. Bi
The precise measurements of cosmic ray (CR) fluxes and ratios by AMS-02 enable significantly improved constraints on the propagation models of cosmic rays. Recently the AMS-02 collaboration reported high precision measurement of the Boron-to-Carbon ratio (B/C). Together with the proton fluxes and their time evolutions by AMS-02 and PAMELA at earlier time, we re-visit the propagation of CRs in the Milky Way. These sets of data enable us to constrain the parameters of both the injection and propagation simultaneously, as well as a better characterization of the solar modulation effect with the time-evolved spectra. We study a comprehensive set of propagation models, with/without the reacceleration or convection effect. We find that generally reacceleration models fit the proton and B/C data better than non-reacceleration ones. However, the reacceleration models over-predict low energy secondary positrons when compared with the data. The rigidity dependence slope of the diffusion coefficient, $\delta$, is found to be about $0.38-0.50$ for reacceleration models, which slightly favors the Kraichnan type of interstellar turbulence but can not exclude the Kolmogorov case turbulence. The plain diffusion and diffusion-convection models are consistent with the positron data, but fit the nuclei data poorly. Our results suggest that the propagation of nuclei, in either the Milky Way or the solar heliosphere, may be different from that of leptons.