Testing diffusion of cosmic rays in the heliosphere with proton and helium data from AMS

Abstract

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 $R\lesssim$ 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 $\beta \times \lambda (R)$ 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/mass dependent effects in the time-dependent modulation of low-rigidity particles.

5 pages, 3 figures, matches published version

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Cited by in corpus (8)

• Validation of the neutron monitor yield function using data from AMS-02 experiment, 2011--2017
• Time dependence of the flux of helium nuclei in cosmic rays measured by the PAMELA experiment between July 2006 and December 2009
• Numerical modeling of cosmic-ray transport in the heliosphere and interpretation of the proton-to-helium ratio in Solar Cycle 24
• Direct measurements of cosmic rays (TeV and beyond) in space using an ultra-thin homogeneous calorimeter
• Local interstellar spectra and solar modulation of cosmic ray electrons and positrons
• Solar modulation of cosmic proton and helium with AMS-02
• Test of validity of the force-field approximation with AMS-02 and PAMELA monthly fluxes
• Time dependence of the p/He ratio in cosmic rays according to the force-field approximation