A. Aab, Universität Siegen
P. Abreu, Universidade de Lisboa
M. Aglietta, Istituto Nazionale Di Astrofisica, Rome
I. Al Samarai, Laboratoire de Physique Nucléaire et de Hautes Energies
I. F.M. Albuquerque, Universidade de São Paulo
I. Allekotte, Centro Atomico Bariloche
A. Almela, Centro Atomico Constituyentes
J. Alvarez Castillo, Universidad Nacional Autónoma de México
J. Alvarez-Muñiz, Universidad de Santiago de Compostela
M. Ambrosio, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
G. A. Anastasi, Gran Sasso Science Institute
L. Anchordoqui, Lehman College
B. Andrada, Centro Atomico Constituyentes
S. Andringa, Universidade de Lisboa
C. Aramo, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
F. Arqueros, Universidad Complutense de Madrid
N. Arsene, Universitatea din Bucuresti
H. Asorey, Centro Atomico Bariloche
P. Assis, Universidade de Lisboa
J. Aublin, Laboratoire de Physique Nucléaire et de Hautes Energies
G. Avila, Pierre Auger Observatory
A. M. Badescu, University Politehnica of Bucharest
A. Balaceanu, Horia Hulubei National Institute of Physics and Nuclear Engineering
R. J. Barreira Luz, Universidade de Lisboa
C. Baus, Karlsruher Institut für Technologie
J. J. Beatty, The Ohio State University
K. H. Becker, Bergische Universität Wuppertal
J. A. Bellido, The University of Adelaide
C. Berat, Universite Grenoble Alpes
M. E. Bertaina, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
X. Bertou, Centro Atomico Bariloche
P. L. Biermann, Max Planck Institute for Radio Astronomy
P. Billoir, Laboratoire de Physique Nucléaire et de Hautes Energies

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We present a search for ultrarelativistic magnetic monopoles with the Pierre Auger observatory. Such particles, possibly a relic of phase transitions in the early Universe, would deposit a large amount of energy along their path through the atmosphere, comparable to that of ultrahigh-energy cosmic rays (UHECRs). The air-shower profile of a magnetic monopole can be effectively distinguished by the fluorescence detector from that of standard UHECRs. No candidate was found in the data collected between 2004 and 2012, with an expected background of less than 0.1 event from UHECRs. The corresponding 90% confidence level (C.L.) upper limits on the flux of ultrarelativistic magnetic monopoles range from 10-19(cm2 sr s)-1 for a Lorentz factor γ=109 to 2.5×10-21(cm2 sr s)-1 for γ=1012. These results - the first obtained with a UHECR detector - improve previously published limits by up to an order of magnitude.

Publication Source (Journal or Book title)

Physical Review D