Measurement of the mass composition of ultra-high-energy cosmic rays at the Pierre Auger Observatory
Eric William Mayotte, Adila Abdul Halim, P. Abreu, M. Aglietta, I. Allekotte, Kévin Almeida Cheminant, Alejandro Almela, Roberto Aloisio, Jaime Álvarez-Muñiz, Juan Ammerman Yebra, Gioacchino Alex Anastasi, Luis A. Anchordoqui, Belén Andrada, S. Andringa, C. Aramo, Paulo Ricardo Araújo Ferreira, Enrico Arnone, Juan Carlos Arteaga Velázquez, Hernán Gonzalo Asorey, P. Assis, Gualberto Avila, Emanuele Avocone, Alina Mihaela Badescu, Alena Bakalová, Alexandru Balaceanu, Felicia Barbato, Adriel Bartz Mocellin, Jose A. Bellido, Corinne Bérat, Mario E. Bertaina, Gopal Bhatta, Marta Bianciotto, Peter L. Biermann, Virginia Binet, Kathrin Bismark, Teresa Bister, J. Biteau, Jiří Blažek, C. Bleve, Johannes Blümer, Martina Boháčová, Denise Boncioli, C. Bonifazi, Luan Bonneau Arbeletche, Nataliia Borodai, J. Brack, P. Gabriel Brichetto Orchera, Florian Lukas Briechle, A. Bueno, S. Buitink, Mario Buscemi, Max Büsken, Anthony Bwembya, K. S. Caballero‐Mora, Sergio Cabana-Freire, Lorenzo Caccianiga, Ioana Caracas, R. Caruso, A. Castellina, Fernando Catalani, G. Cataldi, Lorenzo Cazon, Marcos Cerda, Alessandro Cermenati, J. A. Chinellato, J. Chudoba, L. Chytka, R. W. Clay, Agustín Cobos Cerutti, Roberta Colalillo, Alan Coleman, Maria Rita Coluccia, R. Conceição, Antonio Condorelli, Giovanni Consolati, Matteo Conte, Fabio Convenga, Diego Correia dos Santos, Pedro J. Costa, C. E. Covault, M. Cristinziani, Carlo Salvattore Cruz Sanchez, S. Dasso, K. Daumiller, B. R. Dawson, Rogerio M. de Almeida, Joaquin de Jesus, S. J. de Jong, João de Mello Neto, I. De Mitri, Jaime de Oliveira, Danelise de Oliveira Franco, Francesco de Palma, Vitor de Souza, Emanuele De Vito, Antonino Del Popolo, Olivier Deligny, N. Denner, Luca Deval, Armando di Matteo
Abstract
After nearly 20 years of data-taking, the measurements made with the Pierre Auger Observatory represent the largest collection of ultra-high-energy cosmic ray (UHECR) data so far assembled from a single instrument. Exploring this data set led to a deeper understanding of the UHECR flux and many surprises. In particular, studies aiming to investigate and leverage the mass composition of UHECRs have played an important role in empowering discovery. This contribution will present an overview of the analyses of primary mass composition carried out during the first phase of the Observatory. The overview includes analyses derived from measurements made by the surface, fluorescence, and radio detectors covering energies ranging from 0.1 EeV up to 100 EeV. Special attention will be given to recent advances and results to provide a complete picture of UHECR mass composition at the Observatory as it moves to its next phase, AugerPrime. Additionally, specific updates will be given to studies focusing on mass trends from surface detector rise-times, $𝑋_{\rm max}{}$dependent anisotropies, and UHECR beam characterization using the correlation between $𝑋_{\rm max}{}$and signal amplitudes at the ground.