Browsing by Author "Pierre Auger collaboration (485 authors)"
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- Depth of maximum of air-shower profiles at the Pierre Auger Observatory. I. Measurements at energies above $10^{17.8}$ eVPublication . Pierre Auger collaboration (485 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Brogueira, Pedro; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, Joao; Gonçalves, Patrícia; Oliveira, Micael; Pimenta, Mário; Santo, Catarina E; Santos, Eva; Sarmento, Raul; Tomé, Bernardo
We report a study of the distributions of the depth of maximum, Xmax, of extensive air-shower profiles with energies above 1017.8 eV 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.
- Depth of maximum of air-shower profiles at the Pierre Auger Observatory. II. Composition implicationsPublication . Pierre Auger collaboration (485 authors); Abreu, P.; Andringa, S.; Assis, P.; Brogueira, P.; Cazon, L.; Conceicao, R.; Diogo, F.; Espadanal, J.; Goncalves, P.; Oliveira, M.; Pimenta, M.; Santo, C.E.; Santos, E.; Sarmento, R.; Tome, B.Using the data taken at the Pierre Auger Observatory between December 2004 and December 2012, we have examined the implications of the distributions of depths of atmospheric shower maximum (Xmax), using a hybrid technique, for composition and hadronic interaction models. We do this by fitting the distributions with predictions from a variety of hadronic interaction models for variations in the composition of the primary cosmic rays and examining the quality of the fit. Regardless of what interaction model is assumed, we find that our data are not well described by a mix of protons and iron nuclei over most of the energy range. Acceptable fits can be obtained when intermediate masses are included, and when this is done consistent results for the proton and iron-nuclei contributions can be found using the available models. We observe a strong energy dependence of the resulting proton fractions, and find no support from any of the models for a significant contribution from iron nuclei. However, we also observe a significant disagreement between the models with respect to the relative contributions of the intermediate components.