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Ahn, E. J.; Albuquerque, I. F. M.; Aranda, V. M.; Ave, M.; Avenier, M.; Badescu, A. M.; Bäuml, J.; Berat, C.; Bertaina, M. E.; Billoir, P.; Boháčová, M.; Buitink, S.; Caccianiga, L.; Caramete, L.; Caruso, R.; Cataldi, G.; Cester, R.; Chavez, A. G.; Chiavassa, A.; Coleman, A.; Dallier, R.; Daumiller, K.; de Almeida, R. M.; de Jong, S. J.; de Mello Neto, J. R. T.; Deligny, O.; Di Matteo, A.; Escobar, C. O.; Facal San Luis, P.; Figueira, J. M.; Filevich, A.; García, B.; Ghia, P. L.; Giammarchi, M.; Giller, M.; Gouffon, P.; Grubb, T. D.; Guardincerri, Y.; Haungs, A.; Heck, D.; Heimann, P.; Hörandel, J. R.; Isar, P. G.; Jarne, C.; Kampert, K. H.; Keilhauer, B.; Krömer, O.; Lauer, R.; Leigui de Oliveira, M. A.; Louedec, K.; Maller, J.; Marin, V.; Martello, D.; Mathys, S.; Melo, D.; Mitrica, B.; Molina-Bueno, L.; Mollerach, S.; Montanet, F.; Moura, C. A.; Navarra, G.; Nosek, D.; Olmos-Gilbaja, V. M.; Papenbreer, P.; Parente, G.; Perrone, L.; Petrera, S.; Petrov, Y.; Pimenta, M.; Pirronello, V.; Quel, E. J.; Querchfeld, S.; Ravel, O.; Ravignani, D.; Revenu, B.; Ridky, J.; Risse, M.; Ristori, P.; Roberts, J.; Rosado, J.; Roulet, E.; Rovero, A. C.; Santo, C. E.; Santos, E. M.; Scharf, N.; Schulz, J.; Schumacher, J.; Settimo, M.; Sigl, G.; Śmiałkowski, A.; Šmída, R.; Snow, G. R.; Sutherland, M. S.; Trovato, E.; Verzi, V.; Weindl, A.; Werner, F.; Williams, C.; Wundheiler, B.; Yamamoto, T.
Physical review. D, Particles, fields, gravitation, and cosmology, 02/2015, Letnik: 91, Številka: 3Journal Article
The Pierre Auger collaboration reports new results bearing on the composition of cosmic rays. The muon number of air showers, created by cosmic rays and measured by the collaboration, is intriguingly at odds with all theoretical models, posing a challenge to our current understanding of the mass composition of cosmic rays. We present the first hybrid measurement of the average muon number in air showers at ultrahigh energies, initiated by cosmic rays with zenith angles between 62degrees and 80degrees. The measurement is based on 174 hybrid events recorded simultaneously with the surface detector array and the fluorescence detector of the Pierre Auger Observatory. The muon number for each shower is derived by scaling a simulated reference profile of the lateral muon density distribution at the ground until it fits the data. A 10 super(19) eV shower with a zenith angle of 67degrees, which arrives at the surface detector array at an altitude of 1450 m above sea level, contains on average (2.68 + or - 0.04 + or - 0.48(sys)) x 10 super(7) muons with energies larger than 0.3 GeV. The logarithmic gain d ln N sub( mu )/d ln E of muons with increasing energy between 4 X 10 super(18) eV and 5 x 10 super(19) eV is measured to be (1.029 + or - 0.024 + or - 0.030(sys)).
