Towards solving the mass-composition problem in ultra high energy cosmic rays

Understand

Using the Auger mass-composition analysis of ultra high energy cosmic rays, based on the shape-fitting of $X_{max}$ distributions, we demonstrate that mass composition and energy spectra measured by Auger, Telescope Array and HiRes can be brought into good agreement.

• The shape-fitting analysis of $X_{max}$ distributions shows that the measured sum of proton and Helium fractions, for some hadronic-interaction models, can saturate the total flux.
• Such p+He model, with small admixture of other light nuclei, naturally follows from cosmology with recombination and reheating phases.
• The most radical assumption of the presented model is the assumed unreliability of the experimental separation of Helium and protons, which allows to consider He/p ratio as a free parameter.