The measurement of the average depth of the shower maximum is the most commonly used observable for the possible inference of the primary cosmic-ray mass composition. Currently, different experimental Collaborations process and present their data not in the same way, leading to problems in the comparability and interpretation of the results. Whereas <Xmax> is expected to be proportional to <ln A> in ideal conditions, we demonstrate that the finite field-of-view of fluorescence telescopes plus the attenuation in the atmosphere can introduce a non-linearity into this relation, which is specific for each particular detector setup.
@article{arxiv.1203.1781,
title = {The non-linearity between <ln A> and <Xmax> induced by the acceptance of fluorescence telescopes},
author = {R. Ulrich and L. Cazon},
journal= {arXiv preprint arXiv:1203.1781},
year = {2015}
}