Long-term monitoring of the optical performance of the primary mirrors at the Coihueco and Loma Amarilla sites of the Pierre Auger Observatory
Adila Abdul HalimAdelaide University, Adelaide, S.A.,P. AbreuLaboratório de Instrumentação e Física Experimental de Partículas — LIP and Instituto Superior Técnico — IST, Universidade de Lisboa — UL, Lisboa,M. AgliettaOsservatorio Astrofisico di Torino (INAF), Torino,M. AhmedUniversité Paris-SaclayI. AllekotteCentro Atómico Bariloche and Instituto Balseiro (CNEA-UNCuyo-CONICET), San Carlos de Bariloche,Kévin Almeida CheminantNationaal Instituut voor Kernfysica en Hoge Energie Fysica (NIKHEF), Science Park, Amsterdam,R. ALOISIOGran Sasso Science Institute, L'Aquila,Jaime Álvarez-MuñizInstituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela,Antonio AmbrosoneINFN Laboratori Nazionali del Gran Sasso, Assergi (L'Aquila),Juan Ammerman YebraInstituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela,L. AnchordoquiDepartment of Physics and Astronomy, Lehman College, City University of New York, Bronx, NY,B. AndradaInstituto de Tecnologías en Detección y Astropartículas (CNEA, CONICET, UNSAM), Buenos Aires,L. Andrade DouradoGran Sasso Science Institute, L'Aquila,L. ApollonioINFN, Sezione di Milano, Milano,C. AramoINFN, Sezione di Napoli, Napoli,E. ArnoneUniversità Torino, Dipartimento di Fisica, Torino,J. C. Arteaga‐VelázquezUniversidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacán,P. AssisLaboratório de Instrumentação e Física Experimental de Partículas — LIP and Instituto Superior Técnico — IST, Universidade de Lisboa — UL, Lisboa,G. AvilaObservatorio Pierre Auger and Comisión Nacional de Energía Atómica, Malargüe,Emanuele AvoconeUniversità dell'Aquila, Dipartimento di Scienze Fisiche e Chimiche, L'Aquila,Alena BakalováInstitute of Physics of the Czech Academy of Sciences, Prague,Y. BalibreaObservatorio Pierre Auger and Comisión Nacional de Energía Atómica, Malargüe,A. BalutaCenter for Astrophysics and Cosmology (CAC), University of Nova Gorica, Nova Gorica,Felicia BarbatoGran Sasso Science Institute, L'Aquila,A. Bartz MocellinColorado School of Mines, Golden, CO,J. P. BehlerObservatorio Pierre Auger, Malargüe,Corinne BératM. E. BertainaINFN, Sezione di Torino, Torino,Marta BianciottoUniversità Torino, Dipartimento di Fisica, Torino,Peter L. BiermannV. BinetInstitute of Physics RosarioKathrin BismarkKarlsruhe Institute of Technology (KIT), Institute for Experimental Particle Physics, Karlsruhe,Teresa BisterNationaal Instituut voor Kernfysica en Hoge Energie Fysica (NIKHEF), Science Park, Amsterdam,J. BiteauLaboratoire de Physique des 2 Infinis Irène Joliot-CurieJiří BlažekInstitute of Physics of the Czech Academy of Sciences, Prague,J. BlümerKarlsruhe Institute of Technology (KIT), Institute for Astroparticle Physics, Karlsruhe,M. BoháčováInstitute of Physics of the Czech Academy of Sciences, Prague,Denise BoncioliINFN Laboratori Nazionali del Gran Sasso, Assergi (L'Aquila),C. BonifaziCentro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, RJ,Nataliia BorodaiInstitute of Nuclear Physics PAN, Krakow,J. BrackP. G. Brichetto OrqueraKarlsruhe Institute of Technology (KIT), Institute for Astroparticle Physics, Karlsruhe,A. BuenoUniversidad de Granada and C.A.F.P.E., Granada,S. BuitinkVrije Universiteit Brussels, Brussels,Anthony BwembyaNationaal Instituut voor Kernfysica en Hoge Energie Fysica (NIKHEF), Science Park, Amsterdam,K. S. Caballero‐MoraUniversidad Autónoma de Chiapas, Tuxtla Gutiérrez, Chiapas,S. Cabana-FreireInstituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela,Lorenzo CaccianigaINFN, Sezione di Milano, Milano,J. Caraça-ValenteColorado School of Mines, Golden, CO,R. CarusoUniversità di Catania, Dipartimento di Fisica e Astronomia “Ettore Majorana“, Catania,A. CastellinaOsservatorio Astrofisico di Torino (INAF), Torino,F. CatalaniUniversidade de São Paulo, Escola de Engenharia de Lorena, Lorena, SP,G. CataldiINFN, Sezione di Lecce, Lecce,Lorenzo CazonInstituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela,M. CerdaObservatorio Pierre Auger, Malargüe,B. ČermákováKarlsruhe Institute of Technology (KIT), Institute for Astroparticle Physics, Karlsruhe,A. CermenatiINFN Laboratori Nazionali del Gran Sasso, Assergi (L'Aquila),K. ČernýPalacky University, Olomouc,J. ChinellatoUniversidade Estadual de Campinas (UNICAMP), IFGW, Campinas, SP,J. ChudobaInstitute of Physics of the Czech Academy of Sciences, Prague,L. ChytkaPalacky University, Olomouc,R. W. ClayAdelaide University, Adelaide, S.A.,A. C. Cobos CeruttiInstituto de Tecnologías en Detección y Astropartículas (CNEA, CONICET, UNSAM), and Universidad Tecnológica Nacional — Facultad Regional Mendoza (CONICET/CNEA), Mendoza,Roberta ColalilloUniversità di Napoli “Federico II”, Dipartimento di Fisica “Ettore Pancini”, Napoli,R. ConceiçãoLaboratório de Instrumentação e Física Experimental de Partículas — LIP and Instituto Superior Técnico — IST, Universidade de Lisboa — UL, Lisboa,Giovanni ConsolatiINFN, Sezione di Milano, Milano,M. ConteUniversità del Salento, Dipartimento di Matematica e Fisica “E. De Giorgi”, Lecce,Fabio ConvengaGran Sasso Science Institute, L'Aquila,Diego Correia dos SantosUniversidade Federal do Rio de Janeiro, Instituto de Física, Rio de Janeiro, RJ,Pedro J. CostaLaboratório de Instrumentação e Física Experimental de Partículas — LIP and Instituto Superior Técnico — IST, Universidade de Lisboa — UL, Lisboa,C. E. CovaultCase Western Reserve University, Cleveland, OH,M. CristinzianiUniversität Siegen, Department Physik — Experimentelle Teilchenphysik, Siegen,Carlo Salvattore Cruz SanchezUniversidad Nacional de La PlataS. DassoInstituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), Buenos Aires,K. DaumillerKarlsruhe Institute of Technology (KIT), Institute for Astroparticle Physics, Karlsruhe,B. R. DawsonAdelaide University, Adelaide, S.A.,R. M. de AlmeidaUniversidade Federal do Rio de Janeiro, Instituto de Física, Rio de Janeiro, RJ,E.-T. de BooneFolkwang University of the ArtsBeatriz de ErricoUniversidade Federal do Rio de Janeiro, Instituto de Física, Rio de Janeiro, RJ,Joaquín de JesúsInstituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela,S. J. de JongNationaal Instituut voor Kernfysica en Hoge Energie Fysica (NIKHEF), Science Park, Amsterdam,A. De RoeckUniversidade Federal do Rio de Janeiro, Instituto de Física, Rio de Janeiro, RJ,I. De MitriGran Sasso Science Institute, L'Aquila,Danelise de Oliveira FrancoUniversität Hamburg, II. Institut für Theoretische Physik, Hamburg,F. de PalmaINFN, Sezione di Lecce, Lecce,V. de SouzaUniversidade de São PauloEmanuele De VitoINFN, Sezione di Lecce, Lecce,A. Del PopoloINFN, Sezione di Catania, Catania,O. DelignyCNRS/IN2P3, IJCLab, Université Paris-Saclay, Orsay,N. DennerInstitute of Physics of the Czech Academy of Sciences, Prague,K. Denner SyrokvasCharles University, Faculty of Mathematics and Physics, Institute of Particle and Nuclear Physics, Prague,L. DevalINFN, Sezione di Torino, Torino,A. di MatteoINFN, Sezione di Torino, Torino,C. DobrigkeitUniversidade Estadual de Campinas (UNICAMP), IFGW, Campinas, SP,J. C. D’OlivoUniversidad Nacional Autónoma de México, México, D.F.,Luis Miguel Domingues MendesCentro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, RJ,Y. Dominguez BallesterosUniversidad Industrial de Santander, Bucaramanga,Q. DorostiFolkwang University of the ArtsR. C. dos AnjosUniversidade Federal do Paraná, Setor Palotina, Palotina,Jan EbrInstitute of Physics of the Czech Academy of Sciences, Prague,
2026en
ABI
Abstract
Abstract This paper presents the results of an optical performance monitoring campaign for the primary mirrors installed in fluorescence telescopes at the Coihueco and Loma Amarilla sites at the Pierre Auger Observatory in Argentina. Since the end of 2003, this effort has developed into a unique long-term dataset that addresses the performance of the primary mirrors. We have focused on the scattering characteristics and specular reflectance of mirror segments, as well as their evolution over several years of operation. Despite being housed in climate-controlled buildings, dust accumulation, impurities, and natural aging — such as oxidation or other chemical or physical degradation processes — gradually deteriorate the specular reflectivity of the mirror segments. In this paper, we summarize data collected over eight years of fluorescence telescope operation since the last major cleaning in autumn 2016. During this period, periodic in situ measurements were performed of scattering characteristics using two techniques: (1) specular and diffuse reflectance measurements at a wavelength of 670 nm using a portable scatterometer, and (2) spectral reflectance measurements in the range from 300 nm to 700 nm using an integrating sphere and a spectrometer. This study builds upon a previous monitoring campaign conducted between 2012 and 2017. The measurements show that the primary mirrors remain in acceptable condition after more than 20 years of operation.
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