Recent data on Galactic cosmic rays ( CRs ) revealed that the helium energy spectrum is harder than the proton spectrum .
The AMS experiment has now reported that the proton-to-helium ratio as function of rigidity \R ( momentum-to-charge ratio ) falls off steadily as p/He \propto \R ^ { \Delta } , with \Delta \approx - 0.08 between \R \sim 40 GV and \R \sim 2 TV .
Besides , the single spectra of proton and helium are found to progressively harden at \R \gtrsim 100 GV .
The p/He anomaly is generally ascribed to particle-dependent acceleration mechanisms occurring in Galactic CR sources .
However , this explanation poses a challenge to the known mechanisms of particle acceleration since they are believed to be “ universal ” , composition blind , rigidity mechanisms .
Using the new AMS data , we show that the p/He anomaly can be simply explained in terms of a two-component scenario where the GeV–TeV flux is ascribed to a hydrogen-rich source , possibly a nearby supernova remnant , characterized by a soft acceleration spectrum .
This simple idea provides a common interpretation for the p/He ratio and for the single spectra of proton and helium : both anomalies are explained by a flux transition between two components .
The “ universality ” of particle acceleration in sources is not violated in this model .
A distinctive signature of our scenario is the high-energy flattening of the p/He ratio at multi-TeV energies , which is hinted at by existing data and will be resolutely tested by new space experiments ISS-CREAM and CALET .