Title: Measurements of the depth of maximum of air-shower profiles at the Pierre Auger Observatory and their composition implications,
Abstract: Air-showers measured by the Pierre Auger Observatory were analyzed in order
to extract the depth of maximum (Xmax).The results allow the analysis of the
Xmax distributions as a function of energy ($> 10^{17.8}$ eV). The Xmax
distributions, their mean and standard deviation are analyzed with the help of
shower simulations with the aim of interpreting the mass composition. The mean
and standard deviation were used to derive <ln A> and its variance as a
function of energy. The fraction of four components (p, He, N and Fe) were fit
to the Xmax distributions. Regardless of the hadronic model used the data is
better described by a mix of light, intermediate and heavy primaries. Also,
independent of the hadronic models, a decrease of the proton flux with energy
is observed. No significant contribution of iron nuclei is derived in the
entire energy range studied.