Report of the Working Group on the Composition of Ultra High Energy Cosmic Rays

Abstract

For the first time a proper comparison of the average depth of shower maximum (X max ) published by the Pierre Auger and Telescope Array Observatories is presented. The X max distributions measured by the Pierre Auger Observatory were fit using simulated events initiated by four primaries (proton, helium, nitrogen and iron). The primary abundances which best describe the Auger data were simulated through the Telescope Array (TA) Middle Drum (MD) fluorescence and surface detector array. The simulated events were analyzed by the TA Collaboration using the same procedure as applied to their data. The result is a simulated version of the Auger data as it would be observed by TA. This analysis allows a direct comparison of the evolution of X max with energy of both data sets. The X max measured by TA-MD is consistent with a preliminary simulation of the Auger data through the TA detector and the average difference between the two data sets was found to be (2.9 ± 2.7 (stat.) ± 18 (syst.)) g/cm 2 .

\(\langle X_{\text{max}} \rangle \) Uncertainty from Extrapolation of Cosmic Ray Air Shower Parameters

“…Intermediate weight nuclei are distributed between the proton and iron depths in a logarithmic manner. Currently, the three experiments with the best data on < X max >, the High Resolution Fly s Eye (HiRes) [1], the Telescope Array (TA) [2], and the Pierre Auger Observatory (PAO) [3], all agree within their systematic uncertainties in the actual measurement of < X max > as a function of energy [4].…”

“Lomonosov” Satellite—Space Observatory to Study Extreme Phenomena in Space

“…In the case of the Auger points, the inner error bars denote the statistical uncertainty of the measurement, and the total error bar also includes contributions from the limited statistics of simulated events used for the folding. The colored bands show the systematic uncertainties of the X max scales of each experiment (Abbasi et al 2015b) can be misleading. Namely, the TA collaboration published values of X max obtained from distributions of X max that included detector effects such as selection efficiency and acceptance.…”

“…In the analysis performed by Auger, only shower geometries are selected, allowing sampling of almost unbiased X max distributions. Residual biases from the acceptance, reconstruction and resolution are corrected for Abbasi et al (2015b), Unger (2015). A thorough comparison of the energy evolution of X max as measured by TA and Auger has been performed by the working group.…”

Constraints on violation of Lorentz invariance from atmospheric showers initiated by multi-TeV photons

“…As such, it essentially relies on the assumption that the dominant component of UHE cosmic rays are protons that give rise to UHE photons through a cascade starting with a pion production on CMB -the GZK process [59,60]. At the moment it is not clear whether this assumption actually holds [61].…”