Remarks on the chemical composition of highest-energy cosmic rays
  We present arguments aiming to reconcile the apparently contradictory results concerning the chemical composition of cosmic rays of highest energy, coming recently from Auger and HiRes collaborations. In particular, we argue that the energy dependence of the mean value and root mean square fluctuation of shower maxima distributions observed by the Auger experiment are not necessarily caused by the change of nuclear composition of primary cosmic rays. 
Grzegorz Wilk and Zbigniew Wlodarczyk
astro-ph.HE hep-ph