@misc{10481/104950,
year = {2025},
month = {1},
url = {https://hdl.handle.net/10481/104950},
abstract = {We present measurements of the atmospheric depth of the shower maximum 𝑋�max, inferred for the first time on an event-by-event level using the surface detector of the Pierre Auger Observatory. Using deep learning, we were able to extend measurements of the 𝑋�max distributions up to energies of 100 EeV (1020  eV), not yet revealed by current measurements, providing new insights into the mass composition of cosmic rays at extreme energies. Gaining a 10-fold increase in statistics compared to the fluorescence detector data, we find evidence that the rate of change of the average 𝑋�max with the logarithm of energy features three breaks at 6.5±0.6⁢(stat)±1⁢(syst)  EeV, 11 ±2⁢(stat) ±1⁢(syst)  EeV, and 31 ±5⁢(stat) ±3⁢(syst)  EeV, in the vicinity to the three prominent features (ankle, instep, suppression) of the cosmic-ray flux. The energy evolution of the mean and standard deviation of the measured 𝑋�max distributions indicates that the mass composition becomes increasingly heavier and purer, thus being incompatible with a large fraction of light nuclei between 50 and 100 EeV.},
organization = {Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación (PID2019–105544 GBI00, PID2022-140510NB-I00, and RYC2019-027017-I)},
organization = {Junta de Andalucía (SOMM17/6104/UGR and P18-FR-4314)},
organization = {European Union (Marie Sklodowska-Curie 101065027 and ERDF)},
organization = {European Union - NextGenerationEU (CN_00000013)},
publisher = {American Physical Society},
title = {Inference of the Mass Composition of Cosmic Rays with Energies from 10^18.5 to 10^20  eV Using the Pierre Auger Observatory and Deep Learning},
doi = {10.1103/PhysRevLett.134.021001},
author = {Abdul Halim, A. and Pierre Auger Collaboration, / and Bueno Villar, Antonio},
}