Search for photons above 10<sup>19</sup> eV with the surface detector of the Pierre Auger Observatory
P. Abreu, M. Aglietta, I. Allekotte, Kévin Almeida Cheminant, A. Almela, Jaime Álvarez-Muñiz, Juan Ammerman Yebra, Gioacchino Alex Anastasi, Luis A. Anchordoqui, B. Andrada, S. Andringa, C. Aramo, Paulo Ricardo Araújo Ferreira, E. Arnone, J.C. Arteaga Velázquez, H. Asorey, P. Assis, G. Ávila, Emanuele Avocone, Alina Mihaela Badescu, Alena Bakalová, A. Balaceanu, Felicia Barbato, Jose A. Bellido, C. Berat, М. Бертаина, Gopal Bhatta, Peter L. Biermann, V. Binet, K. Bismark, Teresa Bister, Jonathan Biteau, Jiří Blažek, C. Bleve, J. Blümer, M. Boháčová, Denise Boncioli, C. Bonifazi, L. Bonneau Arbeletche, Nataliia Borodai, J. Brack, T. Bretz, P. Gabriel Brichetto Orchera, F.L. Briechle, P. Buchholz, A. Bueno, S. Buitink, Mario Buscemi, Max Büsken, Anthony Bwembya, K. S. Caballero‐Mora, Lorenzo Caccianiga, I. Caracas, R. Caruso, A. Castellina, F. Catalani, G. Cataldi, Lorenzo Cazon, M. Cerda, J. A. Chinellato, J. Chudoba, L. Chytka, R. W. Clay, A.C. Cobos Cerutti, Roberta Colalillo, A. Coleman, M. R. Coluccia, R. Conceição, A. Condorelli, G. Consolati, F. Contreras, Fabio Convenga, Diego Correia dos Santos, C. E. Covault, M. Cristinziani, S. Dasso, K. Daumiller, B. R. Dawson, R. M. de Almeida, J. 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, Olivier Deligny, L. Deval, A. di Matteo, M. Dobre, C. Dobrigkeit, J.C. D'Olivo, Luis Miguel Domingues Mendes, R. C. dos Anjos, Jan Ebr, M. Eman, R. Engel
Abstract
Abstract We use the surface detector of the Pierre Auger Observatory to search for air showers initiated by photons with an energy above 10 19 eV. Photons in the zenith angle range from 30 ∘ to 60 ∘ can be identified in the overwhelming background of showers initiated by charged cosmic rays through the broader time structure of the signals induced in the water-Cherenkov detectors of the array and the steeper lateral distribution of shower particles reaching ground. Applying the search method to data collected between January 2004 and June 2020, upper limits at 95% CL are set to an E -2 diffuse flux of ultra-high energy photons above 10 19 eV, 2 × 10 19 eV and 4 × 10 19 eV amounting to 2.11 × 10 -3 , 3.12 × 10 -4 and 1.72 × 10 -4 km -2 sr -1 yr -1 , respectively. While the sensitivity of the present search around 2 × 10 19 eV approaches expectations of cosmogenic photon fluxes in the case of a pure-proton composition, it is one order of magnitude above those from more realistic mixed-composition models. The inferred limits have also implications for the search of super-heavy dark matter that are discussed and illustrated.