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

Authors

J. Abraham, National Technological University
Gregory Snow, University of Nebraska - LincolnFollow
Pierre Auger Collaboration

Date of this Version

2010

Comments

Published in PRL 104, 091101 (2010). Copyright © 2010 The American Physical Society. Used by permission.

Abstract

We describe the measurement of the depth of maximum, X_max, 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 (106⁺³⁵_-21) g/cm²/decade below 10^{18.24 ±0.05} eV, and (24 ± 3) g/cm²/decade above this energy. The 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.