Origin of the Proton-to-Helium Ratio Anomaly in Cosmic Rays

Abstract

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 $\sim R^{\Delta }$, 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.

5 pages, 4 figures; matches the published version

References in corpus (8)

• Cosmic-Ray Proton and Helium Spectra from the First CREAM Flight
• Spectral breaks as a signature of cosmic ray induced turbulence in the Galaxy
• Origin of the Cosmic Ray Spectral Hardening
• Cosmic-ray protons, nuclei, electrons, and antiparticles under a two-halo scenario of diffusive propagation
• GeV-TeV cosmic-ray spectral anomaly as due to re-acceleration by weak shocks in the Galaxy
• The Connection Between the Positron Fraction Anomaly and the Spectral Features in Galactic Cosmic-Ray Hadrons
• p, He, and C to Fe cosmic-ray primary fluxes in diffusion models: Source and transport signatures on fluxes and ratios
• Secondary Cosmic Ray Nuclei from Supernova Remnants and Constraints to the Propagation Parameters

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