PROTON AND ANTIPROTON MODULATION IN THE HELIOSPHERE FOR DIFFERENT SOLAR CONDITIONS AND AMS-02 MEASUREMENTS PREDICTION (original) (raw)

Testing diffusion of cosmic rays in the heliosphere with p/He data from AMS

2018

After six years of continuous observations in space, the Alpha Magnetic Spectrometer experiment has released new data on the temporal evolution of the proton and helium fluxes in cosmic rays. These data revealed that the ratio between proton and helium fluxes at the same value of rigidity R=p/Z (momentum/charge ratio) is not constant at R<3 GV. In particular, the ratio is found to decrease steadily during the descending phase of Solar Cycle 24 toward the next minimum. We show that such a behavior is a remarkable signature of the β × λ(R) dependence in the diffusion of cosmic rays in heliosphere, where β is their adimensional speed and λ(R) is their mean free path, a universal function of rigidity for all nuclei. This dependence is responsible for distinctive charge/mass dependent effects in the time-dependent modulation of low-rigidity particles.

Numerical modeling of cosmic-ray transport in the heliosphere and interpretation of the proton-to-helium ratio in Solar Cycle 24

Adv. Space Res. 64 (2019) 2477-2489 , 2019

Thanks to space-borne experiments of cosmic-ray (CR) detection, such as the AMS and PAMELA missions in low-Earth orbit, or the Voyager-1 spacecraft in the interstellar space, a large collection of multi-channel and time-resolved CR data has become available. Recently, the AMS experiment has released new precision data, on the proton and helium fluxes in CRs, measured on monthly basis during its first six years of mission. The AMS data reveal a remarkable long-term behavior in the temporal evolution of the proton-to-helium ratio at rigidity R p=Z K ; 3 GV. As we have argued in a recent work, such a behavior may reflect the transport properties of low-rigidity CRs in the inteplanetary space. In particular, it can be caused by mass/charge dependence of the CR diffusion coefficient. In this paper, we present our developments in the numerical modeling of CR transport in the Milky Way and in the heliosphere. Within our model, and with the help of approximated analytical solutions, we describe in details the relations between the properties of CR diffusion and the time-dependent evolution of the proton-to-helium ratio.