Measurement of the depth of maximum of air-shower profiles with energies between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>18.5</mml:mn> </mml:msup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>20</mml:mn> </mml:msup> <mml:mtext> </mml:mtext> <mml:mtext> </mml:mtext> <mml:mi>eV</mml:mi> </mml:math> using the surface detector of the Pierre Auger Observatory and deep learning
Adila Abdul Halim, P. Abreu, M. Aglietta, I. Allekotte, Kévin Almeida Cheminant, A. Almela, Roberto Aloisio, J. Alvarez-Muñiz, Juan Ammerman Yebra, Gioacchino Alex Anastasi, L. Anchordoqui, B. Andrada, Luciana Andrade Dourado, S. Andringa, L. Apollonio, C. Aramo, P. R. Araújo Ferreira, E. Arnone, J. C. Arteaga Velázquez, P. Assis, G. Ávila, Emanuele Avocone, Alena Bakalová, Felicia Barbato, Adriel Bartz Mocellin, Corinne Bérat, M. E. Bertaina, Gopal Bhatta, Marta Bianciotto, Peter L. Biermann, V. Binet, Kathrin Bismark, Teresa Bister, Jonathan Biteau, J. Blazek, C. Bleve, J. Blümer, M. Boháčová, Denise Boncioli, C. Bonifazi, Luan Bonneau Arbeletche, Nataliia Borodai, J. Brack, P. G. Brichetto Orchera, F. L. Briechle, A. Bueno, S. Buitink, Mario Buscemi, Max Büsken, Anthony Bwembya, K. S. Caballero‐Mora, S. Cabana-Freire, Lorenzo Caccianiga, F. Campuzano, R. Caruso, A. Castellina, F. Catalani, G. Cataldi, Lorenzo Cazon, M. Cerda, Berenika Čermáková, A. Cermenati, J. A. Chinellato, J. Chudoba, L. Chytka, R. W. Clay, A. C. Cobos Cerutti, R. Colalillo, M. R. Coluccia, R. Conceição, Antonio Condorelli, Giovanni Consolati, M. Conte, Fabio Convenga, D. Correia dos Santos, Pedro J. Costa, C. E. Covault, M. Cristinziani, Carlo Salvattore Cruz Sanchez, S. Dasso, K. Daumiller, B. R. Dawson, R. M. de Almeida, Beatriz de Errico, Joaquín de Jesús, S. J. de Jong, J. R. T. de Mello Neto, I. De Mitri, J. de Oliveira, Danelise de Oliveira Franco, F. de Palma, V. de Souza, Emanuele De Vito, A. Del Popolo, O. Deligny, N. Denner, L. Deval, A. di Matteo, A John Joel, M. Dobre
Abstract
We report an investigation of the mass composition of cosmic rays with energies from 3 to 100 EeV ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mn>1</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi>EeV</a:mi> <a:mo>=</a:mo> <a:msup> <a:mrow> <a:mn>10</a:mn> </a:mrow> <a:mrow> <a:mn>18</a:mn> </a:mrow> </a:msup> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi>eV</a:mi> </a:mrow> </a:math> ) using the distributions of the depth of shower maximum <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msub> <c:mi>X</c:mi> <c:mi>max</c:mi> </c:msub> </c:math> . The analysis relies on <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mo>∼</e:mo> <e:mn>50</e:mn> <e:mo>,</e:mo> <e:mn>000</e:mn> </e:math> events recorded by the surface detector of the Pierre Auger Observatory and a deep-learning-based reconstruction algorithm. Above energies of 5 EeV, the dataset offers a 10-fold increase in statistics with respect to fluorescence measurements at the Observatory. After cross-calibration using the fluorescence detector, this enables the first measurement of the evolution of the mean and the standard deviation of the <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:msub> <g:mi>X</g:mi> <g:mi>max</g:mi> </g:msub> </g:math> distributions up to 100 EeV. Our findings are threefold: (i) The evolution of the mean logarithmic mass toward a heavier composition with increasing energy can be confirmed and is extended to 100 EeV. (ii) The evolution of the fluctuations of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:msub> <i:mi>X</i:mi> <i:mi>max</i:mi> </i:msub> </i:math> toward a heavier and purer composition with increasing energy can be confirmed with high statistics. We report a rather heavy composition and small fluctuations in <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msub> <k:mi>X</k:mi> <k:mi>max</k:mi> </k:msub> </k:math> at the highest energies. (iii) We find indications for a characteristic structure beyond a constant change in the mean logarithmic mass, featuring three breaks that are observed in proximity to the ankle, instep, and suppression features in the energy spectrum.