http://particle.astro.ru.nl/pub/JPPNP63-293.pdf

Cosmic rays from the knee to the highest energies

The composition of ultra-high-energy cosmic rays is measured with the High Resolution Fly's Eye cosmic-ray observatory data using the Xmax 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 Xmax and 13% in energy. The Xmax elongation rate between 1018.0 and 1019.4 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 Xmax 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.

https://iopscience.iop.org/article/10.1086/427931/pdf

A Study of the Composition of Ultra-High-Energy Cosmic Rays Using the High-Resolution Fly’s Eye

A study of the composition of ultra-high-energy cosmic rays using the High-Resolution Fly's Eye

We conduct a review of experimental results on ultra-high energy cosmic rays (UHECRs) including measurements of the features of the spectrum, the composition of the primary particle flux and the search for anisotropy in event arrival direction. We find that while there is a general consensus on the features in the spectrum—the Second Knee, the Ankle and (to a lesser extent) the GZK Cutoff—there is little consensus on the composition of the primaries that accompany these features. This lack of consensus on the composition makes interpretation of the agreed upon features problematic. There is also little direct evidence about potential sources of UHECRs, as early reports of arrival-direction anisotropies have not been confirmed in independent measurements.

http://iopscience.iop.org/article/10.1088/0954-3899/34/10/R01/pdf

Cosmic rays: The Second Knee and beyond

Nonbirefringent modified-Maxwell theory, coupled to standard Dirac particles, involves nine dimensionless parameters, which can be bounded by the inferred absence of vacuum Cherenkov radiation for ultrahigh-energy cosmic rays (UHECRs). With selected UHECR events, two-sided bounds on the eight nonisotropic parameters are obtained at the 10{sup -18} level, together with an improved one-sided bound on the single isotropic parameter at the 10{sup -19} level.

C. Sinnis

Papers

Search for global dipole enhancements in the HiRes-I monocular data above 1018.5 eV