@article{3074406,
    title = "An upper limit to the photon fraction in cosmic rays above 1019 eV from the Pierre Auger Observatory",
    author = "Abraham, J. and Aglietta, M. and Aguirre, C. and Allard, D. and Allekotte, I. and Allison, P. and Alvarez, C. and Alvarez-Muñiz, J. and Ambrosio, M. and Anchordoqui, L. and Anjos, J.C. and Aramo, C. and Arisaka, K. and Armengaud, E. and Arneodo, F. and Arqueros, F. and Asch, T. and Asorey, H. and Atulugama, B.S. and Aublin, J. and Ave, M. and Avila, G. and Bacelar, J. and Bäcker, T. and Badagnani, D. and Barbosa, A.F. and Barbosa, H.M.J. and Barkhausen, M. and Barnhill, D. and Barroso, S.L.C. and Bauleo, P. and Beatty, J. and Beau, T. and Becker, B.R. and Becker, K.H. and Bellido, J.A. and BenZvi, S. and Berat, C. and Bergmann, T. and Bernardini, P. and Bertou, X. and Biermann, P.L. and Billoir, P. and Blanch-Bigas, O. and Blanco, F. and Blasi, P. and Bleve, C. and Blümer, H. and Boghrat, P. and Boháčová, M. and Bonifazi, C. and Bonino, R. and Boratav, M. and Brack, J. and Brunet, J.M. and Buchholz, P. and Busca, N.G. and Caballero-Mora, K.S. and Cai, B. and Camin, D.V. and Capdevielle, J.N. and Caruso, R. and Castellina, A. and Cataldi, G. and Cazón, L. and Cester, R. and Chauvin, J. and Chiavassa, A. and Chinellato, J.A. and Chou, A. and Chye, J. and Claes, D. and Clark, P.D.J. and Clay, R.W. and Clay, S.B. and Connolly, B. and Cordier, A. and Cotti, U. and Coutu, S. and Covault, C.E. and Cronin, J. and Dagoret-Campagne, S. and Dang Quang, T. and Darriulat, P. and Daumiller, K. and Dawson, B.R. and de Almeida, R.M. and de Carvalho, L.A. and De Donato, C. and de Jong, S.J. and de Mello Jr., W.J.M. and de Mello Neto, J.R.T. and De Mitri, I. and de Oliveira, M.A.L. and de Souza, V. and del Peral, L. and Deligny, O. and Della Selva, A. and Delle Fratte, C. and Dembinski, H. and Di Giulio, C. and Diaz, J.C. and Dobrigkeit, C. and D'Olivo, J.C. and Dornic, D. and Dorofeev, A. and Dova, M.T. and D'Urso, D. and DuVernois, M.A. and Engel, R. and Epele, L. and Erdmann, M. and Escobar, C.O. and Etchegoyen, A. and Ewers, A. and Facal San Luis, P. and Falcke, H. and Fauth, A.C. and Fazio, D. and Fazzini, N. and Fernández, A. and Ferrer, F. and Ferry, S. and Fick, B. and Filevich, A. and Filipčič, A. and Fleck, I. and Fokitis, E. and Fonte, R. and Fuhrmann, D. and Fulgione, W. and García, B. and Garcia-Pinto, D. and Garrard, L. and Garrido, X. and Geenen, H. and Gelmini, G. and Gemmeke, H. and Geranios, A. and Ghia, P.L. and Giller, M. and Gitto, J. and Glass, H. and Gobbi, F. and Gold, M.S. and Gomez Albarracin, F. and Gómez Berisso, M. and Gómez Herrero, R. and Gonçalves do Amaral, M. and Gongora, J.P. and Gonzalez, D. and Gonzalez, J.G. and González, M. and Góra, D. and Gorgi, A. and Gouffon, P. and Grassi, V. and Grillo, A. and Grunfeld, C. and Grupen, C. and Guarino, F. and Guedes, G.P. and Gutiérrez, J. and Hague, J.D. and Hamilton, J.C. and Harakeh, M.N. and Harari, D. and Harmsma, S. and Hartmann, S. and Harton, J.L. and Healy, M.D. and Hebbeker, T. and Heck, D. and Hojvat, C. and Homola, P. and Hörandel, J. and Horneffer, A. and Horvat, M. and Hrabovský, M. and Iarlori, M. and Insolia, A. and Kaducak, M. and Kalashev, O. and Kampert, K.H. and Keilhauer, B. and Kemp, E. and Klages, H.O. and Kleifges, M. and Kleinfeller, J. and Knapik, R. and Knapp, J. and Koang, D.-H. and Kolotaev, Y. and Kopmann, A. and Krömer, O. and Kuhlman, S. and Kuijpers, J. and Kunka, N. and Kusenko, A. and Lachaud, C. and Lago, B.L. and Lebrun, D. and LeBrun, P. and Lee, J. and Letessier-Selvon, A. and Leuthold, M. and Lhenry-Yvon, I. and Longo, G. and López, R. and Lopez Agüera, A. and Lucero, A. and Maldera, S. and Malek, M. and Maltezos, S. and Mancarella, G. and Manceñido, M.E. and Mandat, D. and Mantsch, P. and Mariazzi, A.G. and Maris, I.C. and Martello, D. and Martinez, N. and Martínez, J. and Martínez, O. and Mathes, H.J. and Matthews, J. and Matthews, J.A.J. and Matthiae, G. and Maurin, G. and Maurizio, D. and Mazur, P.O. and McCauley, T. and McEwen, M. and McNeil, R.R. and Medina, G. and Medina, M.C. and Medina Tanco, G. and Meli, A. and Melo, D. and Menichetti, E. and Menshikov, A. and Meurer, Chr. and Meyhandan, R. and Micheletti, M.I. and Miele, G. and Miller, W. and Mollerach, S. and Monasor, M. and Monnier Ragaigne, D. and Montanet, F. and Morales, B. and Morello, C. and Moreno, E. and Morris, C. and Mostafá, M. and Muller, M.A. and Mussa, R. and Navarra, G. and Nellen, L. and Newman-Holmes, C. and Newton, D. and Nguyen Thi, T. and Nichol, R. and Nierstenhöfer, N. and Nitz, D. and Nogima, H. and Nosek, D. and Nožka, L. and Oehlschläger, J. and Ohnuki, T. and Olinto, A. and Oliveira, L.F.A. and Olmos-Gilbaja, V.M. and Ortiz, M. and Ostapchenko, S. and Otero, L. and Palatka, M. and Pallotta, J. and Parente, G. and Parizot, E. and Parlati, S. and Patel, M. and Paul, T. and Payet, K. and Pech, M. and Pȩkala, J. and Pelayo, R. and Pepe, I.M. and Perrone, L. and Petrera, S. and Petrinca, P. and Petrov, Y. and Pham Ngoc, D. and Pham Thi, T.N. and Piegaia, R. and Pierog, T. and Pisanti, O. and Porter, T.A. and Pouryamout, J. and Prado Jr., L. and Privitera, P. and Prouza, M. and Quel, E.J. and Rautenberg, J. and Reis, H.C. and Reucroft, S. and Revenu, B. and Řídký, J. and Risi, A. and Risse, M. and Rivière, C. and Rizi, V. and Robbins, S. and Roberts, M. and Robledo, C. and Rodriguez, G. and Rodríguez Frías, D. and Rodriguez Martino, J. and Rodriguez Rojo, J. and Ros, G. and Rosado, J. and Roth, M. and Roucelle, C. and Rouillé-d'Orfeuil, B. and Roulet, E. and Rovero, A.C. and Salamida, F. and Salazar, H. and Salina, G. and Sánchez, F. and Santander, M. and Santos, E.M. and Sarkar, S. and Sato, R. and Scherini, V. and Schmidt, T. and Scholten, O. and Schovánek, P. and Schüssler, F. and Sciutto, S.J. and Scuderi, M. and Semikoz, D. and Sequeiros, G. and Shellard, R.C. and Siffert, B.B. and Sigl, G. and Skelton, P. and Slater, W. and Smetniansky De Grande, N. and Smiałkowski, A. and Šmída, R. and Smith, B.E. and Snow, G.R. and Sokolsky, P. and Sommers, P. and Sorokin, J. and Spinka, H. and Strazzeri, E. and Stutz, A. and Suarez, F. and Suomijärvi, T. and Supanitsky, A.D. and Swain, J. and Szadkowski, Z. and Tamashiro, A. and Tamburro, A. and Tascau, O. and Ticona, R. and Timmermans, C. and Tkaczyk, W. and Todero Peixoto, C.J. and Tonachini, A. and Torresi, D. and Travnicek, P. and Tripathi, A. and Tristram, G. and Tscherniakhovski, D. and Tueros, M. and Tunnicliffe, V. and Ulrich, R. and Unger, M. and Urban, M. and Valdés Galicia, J.F. and Valiño, I. and Valore, L. and van den Berg, A.M. and van Elewyck, V. and Vazquez, R.A. and Veberič, D. and Veiga, A. and Velarde, A. and Venters, T. and Verzi, V. and Videla, M. and Villaseñor, L. and Vo Van, T. and Vorobiov, S. and Voyvodic, L. and Wahlberg, H. and Wainberg, O. and Waldenmaier, T. and Walker, P. and Warner, D. and Watson, A.A. and Westerhoff, S. and Wiebusch, C. and Wieczorek, G. and Wiencke, L. and Wilczyńska, B. and Wilczyński, H. and Wileman, C. and Winnick, M.G. and Xu, J. and Yamamoto, T. and Younk, P. and Zas, E. and Zavrtanik, D. and Zavrtanik, M. and Zech, A. and Zepeda, A. and Zha, M. and Ziolkowski, M.",
    journal = "ASTROPARTICLE PHYSICS",
    year = "2007",
    volume = "27",
    number = "2-3",
    pages = "155-168",
    publisher = "Elsevier",
    issn = "0927-6505",
    doi = "10.1016/j.astropartphys.2006.10.004",
    keywords = "Auger electron spectroscopy;  Fluorescence;  Photons, Extensive air showers;  Pierre Auger Observatory;  Ultra high energy photons, Cosmic rays",
    abstract = "An upper limit of 16% (at 95% c.l.) is derived for the photon fraction in cosmic rays with energies greater than 1019 eV, based on observations of the depth of shower maximum performed with the hybrid detector of the Pierre Auger Observatory. This is the first such limit on photons obtained by observing the fluorescence light profile of air showers. This upper limit confirms and improves on previous results from the Haverah Park and AGASA surface arrays. Additional data recorded with the Auger surface detectors for a subset of the event sample support the conclusion that a photon origin of the observed events is not favored. © 2006 Elsevier B.V. All rights reserved."
}