A Comparison of Cosmic Ray Composition Measurements at the Highest Energies

Original · EN

In recent years the Fly's Eye and Akeno groups have presented analyses of the cosmic ray mass composition at energies above 10¹7 eV. While the analysis of the Fly's Eye group points to a likely change in mass composition from heavy to light at energies above 10¹8 eV, the Akeno analysis favours an unchanging composition. However, the two groups base their conclusions on simulations using quite different hadronic models. Here we present a comparison of the experiments using the same hadronic model and find that the agreement between the experiments is much improved. Under this model, both experiments measure a composition rich in iron around 10¹7 eV which becomes lighter at higher energies. However, the agreement is not complete, which indicates scope for improvement of the interaction model, or perhaps the need for a re-examination of the experimental results.