Measurement of the proton-air cross-section at sqrt(s) = 57 TeV with the   Pierre Auger Observatory
  Using measured events from the fluorescence detector of the Pierre Auger Observatory, an unbiased distribution of the atmospheric slant depths where showers reach their maxima has been obtained. Analyzing the tail of this distribution the proton-air cross-section for particle production at center-of-mass energies per nucleon of 57 TeV is determined to be [505$\pm$22(stat)+28$-$36(syst)] mb. Systematic uncertainties in the analysis arise from the limited knowledge of the primary mass composition, the need to use shower simulations and the selection of events. For the purpose of making comparisons with accelerator data we also calculate the inelastic and total proton-proton cross-sections using an extended Glauber model. 
Jan Ebr (for the Pierre Auger Collaboration)
hep-ex astro-ph.HE