The Pierre Auger Observatory II: Studies of Cosmic Ray Composition and   Hadronic Interaction models
  Studies of the composition of the highest energy cosmic rays with the Pierre Auger Observatory, including examination of hadronic physics effects on the structure of extensive air showers. 
The Pierre Auger Collaboration: P. Abreu, M. Aglietta, E.J. Ahn,   I.F.M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P....
astro-ph.HE hep-ex