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

Understand

For the first time a proper comparison of the average depth of shower maximum ($X_{\rm max}$) published by the Pierre Auger and Telescope Array Observatories is presented.

• The $X_{\rm max}$ 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.