Indications of Proton-Dominated Cosmic-Ray Composition above 1.6 EeV

R. U. Abbasi et al. (The High Resolution Fly’s Eye Collaboration)
Phys. Rev. Lett. 104, 161101 – Published 20 April 2010; Erratum Phys. Rev. Lett. 104, 199902 (2010)

Abstract

We report studies of ultrahigh-energy cosmic-ray composition via analysis of depth of air shower maximum (Xmax), for air shower events collected by the High-Resolution Fly’s Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate dXmax/d[log(E)] of 47.9±6.0(stat)±3.2(syst)g/cm2/decade 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 4×1018eV.

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  • 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

Erratum

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Vol. 104, Iss. 16 — 23 April 2010

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