The Pierre Auger Project and Enhancements

The current status of the scientific results of the Auger Observatory will be discussed which include spectrum, anisotropy in arrival directions, chemical composition analyses, and limits on neutrino and photon fluxes. A review of the Observatory detection systems will be presented. Auger has started the construction of its second phase which encompasses antennae for radio detection of cosmic rays, high-elevation telescopes, and surface plus muon detectors. Details will be presented on the latter, AMIGA (Auger Muons and Infill for the Ground Array), an Auger project consisting of 85 detector pairs each one composed of a surface water-Cherenkov detector and a buried muon counter. The detector pairs are arranged in an array with spacings of 433 and 750 m in order to perform a detailed study of the 10^17 eV to 10^19 eV spectrum region. Preliminary results on the performance of the 750 m array of surface detectors and the first muon counter prototype will be presented.Comment: 10 pages, 8 figures, VIII Latin American Symposium on Nuclear Physics and Applications December 15-19, 2009, Santiago, Chil

Muon deficit in simulations of air showers inferred from AGASA data

Multiple experiments reported evidences of a muon deficit in air shower simulations with respect to data, which increases with the primary energy. In this work, we study the muon deficit using measurements of the muon density at 1000 m from the shower axis obtained by the Akeno Giant Air Shower Array (AGASA). The selected events have reconstructed energies in the range $18.83\,\leq\,\log_{10}(E_{R}/\textrm{eV})\,\leq\,19.46$ and zenith angles $\theta\leq 36^{\circ}$. We compare these muon density measurements to proton, iron, and mixed composition scenarios, obtained by using the high-energy hadronic interaction models EPOS-LHC, QGSJetII-04, and Sibyll2.3c. We find that AGASA data are compatible with a heavier composition, lying above the predictions of the mixed composition scenarios. The average muon density divided by the energy in AGASA data is greater than in the mixed composition scenarios by a factor of $1.49\pm0.11\,\textrm{(stat)}\pm^{0.49}_{0.30}\,\textrm{(syst)}$, $1.54\pm0.12\,\textrm{(stat)}\pm^{0.50}_{0.31}\,\textrm{(syst)}$, and $1.66\pm0.13\,\textrm{(stat)} \pm ^{0.54}_{0.34}\,\textrm{(syst)}$ for EPOS-LHC, Sibyll2.3c, and QGSJetII-04, respectively. We interpret this as further evidence of a muon deficit in air shower simulations at the highest energies

Muon deficit in simulations of air showers inferred from AGASA data

Multiple experiments reported evidences of a muon deficit in air shower simulations with respect to data, which increases with the primary energy. In this work, we study the muon deficit using measurements of the muon density at 1000 m from the shower axis obtained by the Akeno Giant Air Shower Array (AGASA). The selected events have reconstructed energies in the range $18.83\,\leq\,\log_{10}(E_{R}/\textrm{eV})\,\leq\,19.46$ and zenith angles $\theta\leq 36^{\circ}$. We compare these muon density measurements to proton, iron, and mixed composition scenarios, obtained by using the high-energy hadronic interaction models EPOS-LHC, QGSJetII-04, and Sibyll2.3c. We find that AGASA data are compatible with a heavier composition, lying above the predictions of the mixed composition scenarios. The average muon density divided by the energy in AGASA data is greater than in the mixed composition scenarios by a factor of $1.49\pm0.11\,\textrm{(stat)}\pm^{0.49}_{0.30}\,\textrm{(syst)}$, $1.54\pm0.12\,\textrm{(stat)}\pm^{0.50}_{0.31}\,\textrm{(syst)}$, and $1.66\pm0.13\,\textrm{(stat)} \pm ^{0.54}_{0.34}\,\textrm{(syst)}$ for EPOS-LHC, Sibyll2.3c, and QGSJetII-04, respectively. We interpret this as further evidence of a muon deficit in air shower simulations at the highest energies

Composition determination of cosmic rays from the muon content of the showers

The origin and nature of ultra high energy cosmic rays remains being a mystery. However, great progress has been made in recent years due to the observations performed by the Pierre Auger Observatory and Telescope Array. In particular, it is believed that the composition information of the cosmic rays as a function of the energy can play a fundamental role for the understanding of their origin. The best indicators for primary mass composition are the muon content of extensive air shower and the atmospheric depth of the shower maximum. In this work we consider a maximum likelihood method to perform mass composition analyses based on the number of muons measured by underground muon detectors. The analyses are based on numerical simulations of the showers. The effects introduced by the detectors and the methods used to reconstruct the experimental data are also taken into account through a dedicated simulation that uses as input the information of the simulated showers. In order to illustrate the use of the method, we consider AMIGA (Auger Muons and Infill for the Ground Array), the low energy extension of the Pierre Auger Observatory that directly measures the muonic content of extensive air showers. We also study in detail the impact of the use of different high energy hadronic interaction models in the composition analyses performed. It is found that differences of a few percent between the predicted number of muons have a significant impact on composition determination.Comment: 10 pages, 8 figure