Can strangelets solve the muon puzzle?

In order to examine a muon excess observed by the Pierre Auger Observatory, detailed Monte Carlo simulations were carried out, assuming the existence of strangelets (hypothetical stable lumps of strange quark matter) in the primary cosmic rays. We obtain a rough agreement between the simulations and the data for ordinary nuclei without any contribution of strangelets in the primary flux of cosmic rays.

High energy cosmic ray interactions and UHECR composition problem

The differences between contemporary Monte Carlo generators of high energy hadronic interactions are discussed and their impact on the interpretation of experimental data on ultra-high energy cosmic rays (UHECRs) is studied. Key directions for further model improvements are outlined. The prospect for a coherent interpretation of the data in terms of the UHECR composition is investigated.

Ultrahigh-energy cosmic rays: Anomalies, QCD, and LHC data

Measurements of proton and nuclear collisions at the Large Hadron Collider at nucleon-nucleon c.m. energies up to $ \sqrt {S_{NN} } = 13\,{\rm{TeV}} $ have improved our understanding of hadronic interactions at the highest energies reached in collisions of cosmic rays with nuclei in the earth atmosphere, up to $ \sqrt {S_{NN} } $ ≈ 450 TeV. The Monte Carlo event generators (epos, qgsjet, and sibyll) commonly used to describe the air showers generated by ultrahigh-energy cosmic rays (UHECR, with ECR ≈ 1017-1020 eV) feature now, after parameter retuning based on LHC Run-I data, more consistent predictions on the nature of the cosmic rays at the tail of the measured spectrum. However, anomalies persist in the data that cannot be accommodated by the models. Among others, the total number of muons (as well as their maximum production depth) remains significantly underestimated (overestimated) by all models. Comparisons of epos, qgsjet, and sibyll predictions to the latest LHC data, and to collider MC generators such as pythia, indicate that improved description of hard multiple minijet production and nuclear effects may help reduce part of the data-model discrepancies, shed light on the UHECR composition approaching the observed ECR ≈ 1020 eV cutoff, and uncover any potential new physics responsible for the observed anomalies.