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arXiv · 2406.06315

Inference of the Mass Composition of Cosmic Rays with energies from $\mathbf{10^{18.5}}$ to $\mathbf{10^{20}}$ eV using the Pierre Auger Observatory and Deep Learning

The Pierre Auger Collaboration·A. Abdul Halim·P. Abreu·M. Aglietta·I. Allekotte·K. Almeida Cheminant·A. Almela·R. Aloisio·J. Alvarez-Muñiz·J. Ammerman Yebra·G. A. Anastasi·L. Anchordoqui·B. Andrada·L. Andrade Dourado·S. Andringa·L. Apollonio·C. Aramo·P. R. Araújo Ferreira·E. Arnone·J. C. Arteaga Velázquez·P. Assis·G. Avila·E. Avocone·A. Bakalova·F. Barbato·A. Bartz Mocellin·C. Berat·M. E. Bertaina·G. Bhatta·M. Bianciotto·P. L. Biermann·V. Binet·K. Bismark·T. Bister·J. Biteau·J. Blazek·C. Bleve·J. Blümer·M. Boháčová·D. Boncioli·C. Bonifazi·L. Bonneau Arbeletche·N. Borodai·J. Brack·P. G. Brichetto Orchera·F. L. Briechle·A. Bueno·S. Buitink·M. Buscemi·M. Büsken·A. Bwembya·K. S. Caballero-Mora·S. Cabana-Freire·L. Caccianiga·F. Campuzano·R. Caruso·A. Castellina·F. Catalani·G. Cataldi·L. Cazon·M. Cerda·B. Čermáková·A. Cermenati·J. A. Chinellato·J. Chudoba·L. Chytka·R. W. Clay·A. C. Cobos Cerutti·R. Colalillo·M. R. Coluccia·R. Conceição·A. Condorelli·G. Consolati·M. Conte·F. Convenga·D. Correia dos Santos·P. J. Costa·C. E. Covault·M. Cristinziani·C. S. Cruz Sanchez·S. Dasso·K. Daumiller·B. R. Dawson·R. M. de Almeida·B. de Errico·J. de Jesús·S. J. de Jong·J. R. T. de Mello Neto·I. De Mitri·J. de Oliveira·D. de Oliveira Franco·F. de Palma·V. de Souza·E. De Vito·A. Del Popolo·O. Deligny·N. Denner·L. Deval·A. di Matteo·J. A. do
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Abstract

We present measurements of the atmospheric depth of the shower maximum $X_\mathrm{max}$, 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 $X_\mathrm{max}$ distributions up to energies of 100 EeV ($10^{20}$ 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 $X_\mathrm{max}$ with the logarithm of energy features three breaks at $6.5\pm0.6~(\mathrm{stat})\pm1~(\mathrm{sys})$ EeV, $11\pm 2~(\mathrm{stat})\pm1~(\mathrm{sys})$ EeV, and $31\pm5~(\mathrm{stat})\pm3~(\mathrm{sys})$ 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 $X_\mathrm{max}$ distributions indicates that the mass composition becomes increasingly heavier and purer, thus being incompatible with a large fraction of light nuclei between 50 EeV and 100 EeV.

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The Pierre Auger Collaboration, A. Abdul Halim, P. Abreu, M. Aglietta, I. Allekotte, K. Almeida Cheminant, A. Almela, R. Aloisio, J. Alvarez-Muñiz, J. Ammerman Yebra, G. A. Anastasi, L. Anchordoqui, B. Andrada, L. Andrade Dourado, S. Andringa, L. Apollonio, C. Aramo, P. R. Araújo Ferreira, E. Arnone, J. C. Arteaga Velázquez, P. Assis, G. Avila, E. Avocone, A. Bakalova, F. Barbato, A. Bartz Mocellin, C. Berat, M. E. Bertaina, G. Bhatta, M. Bianciotto, P. L. Biermann, V. Binet, K. Bismark, T. Bister, J. Biteau, J. Blazek, C. Bleve, J. Blümer, M. Boháčová, D. Boncioli, C. Bonifazi, L. Bonneau Arbeletche, N. Borodai, J. Brack, P. G. Brichetto Orchera, F. L. Briechle, A. Bueno, S. Buitink, M. Buscemi, M. Büsken, A. Bwembya, K. S. Caballero-Mora, S. Cabana-Freire, L. Caccianiga, F. Campuzano, R. Caruso, A. Castellina, F. Catalani, G. Cataldi, L. Cazon, M. Cerda, B. Čermáková, A. Cermenati, J. A. Chinellato, J. Chudoba, L. Chytka, R. W. Clay, A. C. Cobos Cerutti, R. Colalillo, M. R. Coluccia, R. Conceição, A. Condorelli, G. Consolati, M. Conte, F. Convenga, D. Correia dos Santos, P. J. Costa, C. E. Covault, M. Cristinziani, C. S. Cruz Sanchez, S. Dasso, K. Daumiller, B. R. Dawson, R. M. de Almeida, B. de Errico, J. de Jesús, S. J. de Jong, J. R. T. de Mello Neto, I. De Mitri, J. de Oliveira, D. de Oliveira Franco, F. de Palma, V. de Souza, E. De Vito, A. Del Popolo, O. Deligny, N. Denner, L. Deval, A. di Matteo, J. A. do. 2024-06-10. Inference of the Mass Composition of Cosmic Rays with energies from $\mathbf{10^{18.5}}$ to $\mathbf{10^{20}}$ eV using the Pierre Auger Observatory and Deep Learning. https://doi.org/10.1103/physrevlett.134.021001

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