Indications of Proton-Dominated Cosmic-Ray Composition above 1.6 EeV
Indications of Proton-Dominated Cosmic-Ray Composition above 1.6 EeV
We report studies of ultra-high energy cosmic ray composition via analysis of depth of airshower maximum (Xmax), for airshower events collected by the High Resolution Fly's Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate d<Xmax>/d(log(E)) of 47.9 +- 6.0 (stat.) +- 3.2 (syst.)g/cm^2/decade for energies …