Jul 12 – 23, 2021
Europe/Berlin timezone

Data-driven Scales of Depth of Shower Maximum and Signals at Ground Level using Hybrid Detection at the Pierre Auger Observatory

Jul 14, 2021, 6:00 PM
1h 30m


Talk CRI | Cosmic Ray Indirect Discussion


Dr Jakub Vícha (Institute of Physics of Czech Academy of Sciences)


Presently large systematic uncertainties still remain in the description of hadronic interactions at ultra-high energies and a fully consistent description of air-shower experimental data is yet to be reached. Specifically, the predictions of the depth of the shower maximum ($X_{\rm max}$) by hadronic interaction models tuned to LHC data differ by around 30 g/cm$^{2}$ at 10$^{19}$ eV. This introduces a lower limit on the uncertainty in the average mass derived from the $X_{\rm max}$ measurements at the level of one third of the difference between protons and iron nuclei. A deficit of the simulated signal with respect to the measured signal in ground detectors is another inconsistency that is usually interpreted as a deficit of the muon signal related to the hadronic component of a simulated shower.

A new global method to simultaneously determine the mass composition of cosmic rays, modifications of the simulated $X_{\rm max}$, and modifications of the hadronic and electromagnetic signals at ground level, is applied to the combined data of the surface and fluorescence detectors at the Pierre Auger Observatory. The data-driven results of the method prefer a deeper scale of simulated $X_{\rm max}$ than predicted by hadronic interaction models EPOS-LHC, QGSJet II-04 and Sibyll 2.3d in the energy range $10^{18.5-19.0}$ eV. Consequently, the mass composition of the primary species was found to be heavier, and the deficit of the simulated hadronic signal at ground level, dominated by muons, is alleviated with respect to the unmodified hadronic interaction models. The standard models fail to describe the measured data without these modifications with a total significance of more than 5$\sigma$.


Cosmic rays; mass composition; models of hadronic interactions; signal in surface detectors; depth of air-shower maximum

Collaboration Auger
Subcategory Experimental Results

Primary author

Dr Jakub Vícha (Institute of Physics of Czech Academy of Sciences)

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