Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV

AUGER COLLABORATION, B. WUNDHEILER

PHYSICAL REVIEW LETTERS

AMER PHYSICAL SOC

Año: 2010 p. 911011 - 911017

0031-9007

We describe the measurement of the depth of maximum, Xmax , of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above 10^18 eV observed by the fluorescencedetector of the Pierre Auger Observatory in coincidence with at least one surface detector station areselected for the analysis. The average shower maximum was found to evolve with energy at a rate of 106+35-21 g/cm^2/decade below 10^18.2+/-0.05 eV, and 24+/-3g/cm^2/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2 . The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.