We report a study of the distributions of the depth of maximum, Xmax, of extensive air-shower profiles with energies above 1017.8eV as observed with the fluorescence telescopes of the Pierre Auger Observatory. The analysis method for selecting a data sample with minimal sampling bias is described in detail as well as the experimental cross-checks and systematic uncertainties. Furthermore, we discuss the detector acceptance and the resolution of the Xmax measurement and provide parametrizations thereof as a function of energy. The energy dependence of the mean and standard deviation of the Xmax distributions are compared to air-shower simulations for different nuclear primaries and interpreted in terms of the mean and variance of the logarithmic mass distribution at the top of the atmosphere.
Publication Source (Journal or Book title)
Physical Review D - Particles, Fields, Gravitation and Cosmology
Aab, A., Abreu, P., Aglietta, M., Ahn, E., Al Samarai, I., Albuquerque, I., Allekotte, I., Allen, J., Allison, P., Almela, A., Alvarez Castillo, J., Alvarez-Muñiz, J., Alves Batista, R., Ambrosio, M., Aminaei, A., Anchordoqui, L., Andringa, S., Aramo, C., Aranda, V., Arqueros, F., Asorey, H., Assis, P., Aublin, J., Ave, M., Avenier, M., Avila, G., Awal, N., Badescu, A., Barber, K., Bäuml, J., Baus, C., Beatty, J., & Becker, K. (2014). Depth of maximum of air-shower profiles at the Pierre Auger Observatory. I. Measurements at energies above 1017.8eV. Physical Review D - Particles, Fields, Gravitation and Cosmology, 90 (12) https://doi.org/10.1103/PhysRevD.90.122005