Testing Diffusion of Cosmic Rays in the Heliosphere with Proton and Helium Data from AMS.

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 less than or similar to 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 beta x lambda(R) dependence in the diffusion of cosmic rays in heliosphere, where beta is their adimensional speed and lambda(R) is their mean free path, a universal function of rigidity for all nuclei. This dependence is responsible for distinctive charge or mass dependent effects in the time-dependent modulation of low-rigidity particles.