Exotic massive hadrons and ultra-high energy cosmic rays
  We investigate the proposal that primary cosmic rays of energy above the Greisen-Zatsepin-Kuzmin cutoff are exotic massive strongly interacting particles (uhecrons). We study the properties of air showers produced by uhecrons and find that masses in excess of about 50 GeV are inconsistent with the highest energy event observed. We also estimate that with sufficient statistics a uhecron of mass as low as 10 GeV may be distinguished from a proton. 
Ivone F.M.Albuquerque, Glennys R.Farrar and Edward W.Kolb