EPJ Web of Conferences
Volume 53, 2013UHECR 2012 - International Symposium on Future Directions in UHECR Physics
|Number of page(s)||6|
|Section||Particle Physics Aspects and Air Shower Phenomenology|
|Published online||25 June 2013|
A measurement of the muon number in showers using inclined events detected at the Pierre Auger Observatory
1 Departamento de Física de Partículas e IGFAE, Universidade de Santiago de Compostela, Spain
2 Observatorio Pierre Auger, Av. San Martin Norte 304, 5613 Malargüe, Argentina
a e-mail: email@example.com
The average muon content of measured showers with zenith angles between 62∘ and 80∘ detected at the Pierre Auger Observatory is obtained as a function of shower energy using a reconstruction method specifically designed for inclined showers and the hybrid character of the detector. The reconstruction of inclined showers relies on a comparison between the measured signals at ground and reference patterns at ground level from which an overall normalization factor is obtained. Since inclined showers are dominated by muons this factor gives the relative muon size. It can be calibrated using a subsample of showers simultaneously recorded with the fluorescence detector (FD) and the surface detector (SD) which provides an independent calorimetric measurement of the energy. The muon size obtained for each shower becomes a measurement of the relative number of muons with respect to the reference distributions. The precision of the measurement is assessed using simulated events which are reconstructed using exactly the same procedure. We compare the relative number of muons versus energy as obtained to simulations. Proton simulations with QGSJETII show a factor of 2.13 ± 0.04(stat) ± 0.11(sys) at 1019eV without significant variations in the energy range explored between 4 × 1018eV to 7 × 1019eV. We find that none of the current shower models, neither for proton nor for iron primaries, are able to predict as many muons as are observed.
© Owned by the authors, published by EDP Sciences, 2013
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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