[1503.07540] Report of the Working Group on the Composition of Ultra High Energy Cosmic Rays:
"For the first time a proper comparison of the average depth of shower maximum (Xmax) published by the Pierre Auger and Telescope Array Observatories is presented. The Xmax 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 ⟨Xmax⟩ with energy of both data sets. The ⟨Xmax⟩ 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/cm2."
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