2025/07/31 by J. Vícha, Alena Bakalová, Vícha, Jakub +7
Physics and Astronomy · Engineering · #Particle Detector Development and Performance #Advanced X-ray and CT Imaging
paper · doi:10.48550/arxiv.2507.23394
The mass composition of ultra-high-energy cosmic rays (UHECRs) is usually inferred from the depth of the shower maximum (X_\rmmax) of cosmic-ray showers, which is only ambiguously determined by modern hadronic interaction models. We present a data-driven interpretation of UHECRs, the heavy-metal scenario, which assumes pure iron nuclei above 1019.6 eV (≈ 40 EeV) as the heaviest observed mass composition and introduces a global shift in the X_\rmmax scale predicted by the two hadronic interaction models QGSJet II-04 and Sibyll 2.3d. We investigate the consequences of the proposed mass-composition model based on the obtained shifts in the X_\rmmax values, which naturally lead to a heavier mass composition of UHECRs than conventionally assumed. We explore the consequences of our model on the energy evolution of relative fractions of primary species, consequently decomposed energy spectrum, hadronic-interaction studies and the arrival directions of UHECRs. We show that within this scenario, presented recently in Vicha et al 2025 ApJL 986 L34, the cosmic-ray measurements can be interpreted in a more consistent way.