@article{7947893454d544ada745ecf007e0647a,
title = "Search for photons with energies above 1018 eV using the hybrid detector of the Pierre Auger Observatory",
abstract = "A search for ultra-high energy photons with energies above 1 EeV is performed using nine years of data collected by the Pierre Auger Observatory in hybrid operation mode. An unprecedented separation power between photon and hadron primaries is achieved by combining measurements of the longitudinal air-shower development with the particle content at ground measured by the fluorescence and surface detectors, respectively. Only three photon candidates at energies 1 - 2 EeV are found, which is compatible with the expected hadroninduced background. Upper limits on the integral flux of ultra-high energy photons of 0.027, 0.009, 0.008, 0.008 and 0.007 km-2 sr-1 yr-1 are derived at 95% C.L. for energy thresholds of 1, 2, 3, 5 and 10 EeV. These limits bound the fractions of photons in the all-particle integral flux below 0.1%, 0.15%, 0.33%, 0.85% and 2.7%. For the first time the photon fraction at EeV energies is constrained at the sub-percent level. The improved limits are below the flux of diffuse photons predicted by some astrophysical scenarios for cosmogenic photon production. The new results rule-out the early top-down models - in which ultra-high energy cosmic rays are produced by, e.g., the decay of super-massive particles - and challenge the most recent super-heavy dark matter models.",
author = "{The Pierre Auger Collaboration} and A. Aab and P. Abreu and M. Aglietta and {Al Samarai}, I. and Albuquerque, {I. F.M.} and I. Allekotte and A. Almela and {Alvarez Castillo}, J. and J. Alvarez-Mu{\~n}iz and Anastasi, {G. A.} and L. Anchordoqui and B. Andrada and S. Andringa and C. Aramo and F. Arqueros and N. Arsene and H. Asorey and P. Assis and J. Aublin and G. Avila and Badescu, {A. M.} and A. Balaceanu and {Barreira Luz}, {R. J.} and Beatty, {J. J.} and Becker, {K. H.} and Bellido, {J. A.} and C. Berat and Bertaina, {M. E.} and X. Bertou and Biermann, {P. L.} and P. Billoir and J. Biteau and Blaess, {S. G.} and A. Blanco and J. Blazek and C. Bleve and M. Boh{\'a}cov{\'a} and D. Boncioli and C. Bonifazi and N. Borodai and Botti, {A. M.} and J. Brack and I. Brancus and T. Bretz and A. Bridgeman and Briechle, {F. L.} and P. Buchholz and A. Bueno and S. Buitink and {Van Vliet}, A.",
note = "Funding Information: The successful installation, commissioning, and operation of the Pierre Auger Observatory would not have been possible without the strong commitment and effort from the technical and administrative staff in Malarg{\"u}e. We are very grateful to the following agencies and organizations for financial support: Argentina - Comisi{\'o}n Nacional de Energ{\'i}a At{\'o}mica; Agencia Nacional de Promoci{\'o}n Cient{\'i}fica y Tecnol{\'o}gica (ANPCyT); Consejo Nacional de Investigaciones Cient{\'i}ficas y T{\'e}cnicas (CONICET); Gobierno de la Provincia de Mendoza; Municipalidad de Malarg{\"u}e; NDM Holdings and Valle Las Le{\~n}as; in gratitude for their continuing cooperation over land access; Australia - the Australian Research Council; Brazil - Conselho Nacional de Desenvolvimento Cient{\'i}fico e Tecnol{\'o}gico (CNPq); Financiadora de Estudos e Projetos (FINEP); Funda{\c c}{\~a}o de Amparo {\`a} Pesquisa do Estado de Rio de Janeiro (FAPERJ); S{\~a}o Paulo Research Foundation (FAPESP) Grants No. 2010/07359-6 and No. 1999/05404-3; Minist{\'e}rio de Ci{\^e}ncia e Tecnologia (MCT); Czech Republic - Grant No. MSMT CR LG15014, LO1305 and LM2015038 and the Czech Science Foundation Grant No. 14-17501S; France - Centre de Calcul IN2P3/CNRS; Centre National de la Recherche Scientifique (CNRS); Conseil R{\'e}gional Ile-de-France; D{\'e}partement Physique Nucl{\'e}aire et Corpusculaire (PNC-IN2P3/CNRS); D{\'e}partement Sciences de l'Univers (SDU-INSU/CNRS); Institut Lagrange de Paris (ILP) Grant No. LABEX ANR- 10-LABX-63 within the Investissements d'Avenir Programme Grant No. ANR-11-IDEX-0004- 02; Germany - Bundesministerium f{\"u}r Bildung und Forschung (BMBF); Deutsche Forschungsgemeinschaft (DFG); Finanzministerium Baden-W{\"u}rttemberg; Helmholtz Alliance for Astroparticle Physics (HAP); Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF); Ministerium f{\"u}r Innovation, Wissenschaft und Forschung des Landes Nordrhein-Westfalen; Ministerium f{\"u}r Wissenschaft, Forschung und Kunst des Landes Baden-W{\"u}rttemberg; Italy - Istituto Nazionale di Fisica Nucleare (INFN); Istituto Nazionale di Astrofisica (INAF); Ministero dell'Istruzione, dell'Universit{\'a} e della Ricerca (MIUR); CETEMPS Center of Excellence; Ministero degli Affari Esteri (MAE); Mexico - Consejo Nacional de Ciencia y Tecnolog{\'i}a (CONACYT) No. 167733; Universidad Nacional Aut{\'o}noma de M{\'e}xico (UNAM); PAPIIT DGAPA-UNAM; The Netherlands - Ministerie van Onderwijs, Cultuur en Wetenschap; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO); Stichting voor Fundamenteel Onderzoek der Materie (FOM); Poland - National Centre for Research and Development, Grants No. ERA-NET-ASPERA/01/11 and No. ERA-NET-ASPERA/02/11; National Sci ence Centre, Grants No. 2013/08/M/ST9/00322, No. 2013/08/M/ST9/00728 and No. HARMONIA 5 - 2013/10/M/ST9/00062; Portugal - Portuguese national funds and FEDER funds within Programa Operacional Factores de Competitividade through Funda{\c c}{\~a}o para a Ci{\^e}ncia e a Tecnologia (COMPETE); Romania - Romanian Authority for Scientific Research ANCS; CNDI-UEFISCDI partnership projects Grants No. 20/2012 and No.194/2012 and PN 16 42 01 02; Slovenia - Slovenian Research Agency; Spain - Comunidad de Madrid; Fondo Europeo de Desarrollo Regional (FEDER) funds; Ministerio de Econom{\'i}a y Competitividad; Xunta de Galicia; European Community 7th Framework Program Grant No. FP7-PEOPLE- 2012-IEF-328826; USA - Department of Energy, Contracts No. DE-AC02-07CH11359, No. DE-FR02-04ER41300, No. DE-FG02-99ER41107 and No. DE-SC0011689; National Science Foundation, Grant No. 0450696; The Grainger Foundation; Marie Curie-IRSES/EPLANET; European Particle Physics Latin American Network; European Union 7th Framework Program, Grant No. PIRSES-2009-GA-246806; and UNESCO.",
year = "2017",
month = apr,
day = "1",
doi = "10.1088/1475-7516/2017/04/009",
language = "British English",
volume = "2017",
journal = "Journal of Cosmology and Astroparticle Physics",
issn = "1475-7516",
publisher = "IOP Publishing Ltd.",
number = "4",
}