Measurement of the Depth of Maximum of Extensive Air Showers above 1018 eV

J. ABRAHAM,...; X. BERTOU

PHYSICAL REVIEW LETTERS

AMER PHYSICAL SOC

Año: 2010 vol. 104 p. 1 - 7

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 1018 eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of ð106þ35Þ g=cm2=decade below 1018:24`0:05 eV, and ð24 ` 3Þ g=cm2=decade above this energy. The ␣21 measured shower-to-shower fluctuations decrease from about 55 to 26 g=cm2. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.