Indications of Proton-Dominated Cosmic Ray Composition above 1.6 EeV
High Energy Astrophysical Phenomena
2010-04-29 v2
Abstract
We report studies of ultra-high energy cosmic ray composition via analysis of depth of airshower maximum (Xmax), for airshower events collected by the High Resolution Fly's Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate d<Xmax>/d(log(E)) of 47.9 +- 6.0 (stat.) +- 3.2 (syst.)g/cm^2/decade for energies between 1.6 EeV 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 EeV.
Keywords
Cite
@article{arxiv.0910.4184,
title = {Indications of Proton-Dominated Cosmic Ray Composition above 1.6 EeV},
author = {R. U. Abbasi and T. Abu-Zayyad and M. Al-Seady and M. Allen and J. F. Amman and R. J. Anderson and G. Archbold and K. Belov and J. W. Belz and D. R. Bergman and S. A. Blake and O. A. Brusova and G. W. Burt and C. Cannon and Z. Cao and W. Deng and Y. Fedorova and C. B. Finley and R. C. Gray and W. F. Hanlon and C. M. Hoffman and M. H. Holzscheiter and G. Hughes and P. Huentemeyer and B. F Jones and C. C. H. Jui and K. Kim and M. A. Kirn and E. C. Loh and J. P. Lundquist and M. M. Maestas and N. Manago and L. J. Marek and K. Martens and J. A. J. Matthews and J. N. Matthews and S. A. Moore and A. O'Neill and C. A. Painter and L. Perera and K. Reil and R. Riehle and M. Roberts and D. Rodriguez and N. Sasaki and S. R. Schnetzer and L. M. Scott and G. Sinnis and J. D. Smith and P. Sokolsky and C. Song and R. W. Springer and B. T. Stokes and S. Stratton and S. B. Thomas and J. R. Thomas and G. B. Thomson and D. Tupa and X. Zhang and A. Zech},
journal= {arXiv preprint arXiv:0910.4184},
year = {2010}
}
Comments
11 pages, 4 figures, accepted for publication in Physical Review Letters