2004/07/31 by s Eye Collaboration, R. U. Abbasi, T. Abu‐Zayyad +53 · 7 citations
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Dark Matter and Cosmic Phenomena #Particle physics theoretical and experimental studies #astro-ph
paper · pdf · doi:10.1086/427931
published as Astrophys.J.622:910-926,2005 · 52 pages, 27 figures. Revised Fig. 10 caption, improved Fig. 23, resubmitted to ApJ. (Previously revised to address referee's comments.) (Originally 37 pages, 13 figures. Submitted to ApJ)
arxiv created 2004/11/24 · openalex publication_date 2005/03/29 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
The composition of ultra-high-energy cosmic rays is measured with the High Resolution Fly's Eye cosmic-ray observatory data using the X max technique. Data were collected in stereo between 1999 November and 2001 September. The data are reconstructed with well-determined geometry. Measurements of the atmospheric transmission are incorporated in the reconstruction. The detector resolution is found to be 30 g cm -2 in X max and 13% in energy. The X max elongation rate between 10 18.0 and 10 19.4 eV is measured to be 54.5 ± 6.5 ± 4.5 g cm -2 per decade. This is compared with predictions using the QGSJet01 and SIBYLL 2.1 hadronic interaction models for both protons and iron nuclei. CORSIKA-generated extensive air showers are incorporated directly into a detailed detector Monte Carlo program. The elongation rate and the X max distribution widths are consistent with a constant or slowly changing and predominantly light composition. A simple model containing only protons and iron nuclei is compared with QGSJet and SIBYLL. The best agreement between the model and the data is for 80% protons for QGSJet and 60% protons for SIBYLL.