Abstract
We present a summary of recent tests and measurements of hadronic interaction properties with air showers. This report has a special focus on muon density measurements. Several experiments reported deviations between simulated and recorded muon densities in extensive air showers, while others reported no discrepancies. We combine data from eight leading air shower experiments to cover shower energies from PeV to tens of EeV. Data are combined using the z-scale, a unified reference scale based on simulated air showers. Energy-scales of experiments are cross-calibrated. Above 10 PeV, we find a muon deficit in simulated air showers for each of the six considered hadronic interaction models. The deficit is increasing with shower energy. For the models EPOS-LHC and QGSJet-II.04, the slope is found significant at 8 sigma.
Highlights
Cosmic rays with energies larger than 1015 eV can only be indirectly observed via extensive air showers
The Pierre Auger Observatory [10, 11] and Telescope Array [12] observed a muon deficit in 1019 eV showers simulated with the latest models
We presented a summary of recent tests and measurements of hadronic interaction properties in air showers with energies from PeV up to tens of EeV
Summary
Cosmic rays with energies larger than 1015 eV can only be indirectly observed via extensive air showers. The width of those bands has two main contributions: the experimental uncertainties, and the uncertainties inherent in converting the air shower observables into lnA , which requires air shower simulations with hadronic interaction models. Tests and measurements of hadronic interaction properties with air showers address these issues They can reduce uncertainties in modeling the air shower development, so that accurate estimates of the cosmic-ray mass can be obtained. They offer opportunities to test the standard model of particle physics under extreme conditions.
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