Authors

J. Abraham, Universidad Tecnologica Nacional
P. Abreu, Instituto Superior Técnico
M. Aglietta, Università degli Studi di Torino
E. J. Ahn, Fermi National Accelerator Laboratory
D. Allard, APC - AstroParticule et Cosmologie
I. Allekotte, Centro Atomico Bariloche
J. Allen, New York University
J. Alvarez-Muñiz, Universidad de Santiago de Compostela
M. Ambrosio, Università degli Studi di Napoli Federico II
L. Anchordoqui, University of Wisconsin-Milwaukee
S. Andringa, Instituto Superior Técnico
T. Antičić, Institute Ruder Boskovic
A. Anzalone, INAF Istituto di Astrofisica Spaziale e Fisica Cosmica di Palermo
C. Aramo, Università degli Studi di Napoli Federico II
E. Arganda, Universidad Complutense de Madrid
K. Arisaka, University of California, Los Angeles
F. Arqueros, Universidad Complutense de Madrid
H. Asorey, Centro Atomico Bariloche
P. Assis, Instituto Superior Técnico
J. Aublin, Laboratoire de Physique Nucléaire et de Hautes Energies
M. Ave, Karlsruher Institut für Technologie, Campus Nord
G. Avila, Comision Nacional de Energia Atomica Argentina
T. Bäcker, Universität Siegen
D. Badagnani, Universidad Nacional de La Plata
M. Balzer, Karlsruher Institut für Technologie, Campus Nord
K. B. Barber, The University of Adelaide
A. F. Barbosa, Centro Brasileiro de Pesquisas Físicas
S. L.C. Barroso, Universidade Estadual do Sudoeste da Bahia
B. Baughman, The Ohio State University
P. Bauleo, Colorado State University
J. J. Beatty, The Ohio State University
B. R. Becker, The University of New Mexico
K. H. Becker, Bergische Universität Wuppertal

Document Type

Article

Publication Date

3-1-2010

Abstract

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 1018eV 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 (106-21+35)g/cm2/decade below 1018.24±0. 05eV, and (24±3)g/cm2/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26g/cm2. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed. © 2010 The American Physical Society.

Publication Source (Journal or Book title)

Physical Review Letters

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