Top-Down analysis at 10^17.5 eV

ANDRADA, B.; SÁNCHEZ, F.

Otro; Pierre Auger Collaboration Internal Note; 2021

In this note we present an analysis using high-quality hybrid events measured with the SD-750 and HeCo with a reconstructed energy of 10^17.5 eV. The work is complementary of previous studies at 10^19.0 eV for which a clear evidence of discrepancy between data and simulations was found and the source of the difference was attributable to the muonic component of the signal. In this analysis, we also found a discrepancy of up to 30%, depending on the considered primary and model, between the simulated SD signal and the observed one. Nevertheless, when we tried to identify the origin of this mismatch, the picture is not so clear as it is at the highest energies. While both considered hadronic interaction models indicate that an energy rescaling of about 10% is needed, the muonic components of the signal show opposite trends: QGSJet-II-04 favors a further increase of 13% in the simulated muonic signal while EPOS-LHC suggests that a decrease of about 22% is needed. To compare this study with previous analysis from Auger and other experiments, we translated the obtained scalings factors to the z parameter. We found that, at 10^17.5 eV, the top-down results are compatible with predictions from Xmax measurements.