Abstract
We report studies of ultrahigh-energy cosmic-ray composition via analysis of depth of air shower maximum (), for air shower events collected by the High-Resolution Fly’s Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate of for energies between 1.6 and 63 EeV, and are consistent with a predominantly protonic composition of cosmic rays when interpreted via the QGSJET01 and QGSJET-II high-energy hadronic interaction models. These measurements constrain models in which the galactic-to-extragalactic transition is the cause of the energy spectrum ankle at .
- Received 21 October 2009
- Corrected 5 May 2010
DOI:https://doi.org/10.1103/PhysRevLett.104.161101
©2010 American Physical Society
Corrections
5 May 2010