Direct measurement of the muonic content of extensive air showers between $$\mathbf { 2\times 10^{17}}$$ and $$\mathbf {2\times 10^{18}}~$$eV at the Pierre Auger Observatory

Abstract

The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between $$2\times 10^{17}$$2×1017 and $$2\times 10^{18}$$2×1018 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at $$10^{{17.5}}\, {\mathrm{eV}} $$1017.5eV and $$10^{{18}}\, {\mathrm{eV}} $$1018eV. We find that, for the models to explain the data, an increase in the muon density of $$38\%$$38%$$\pm 4\% (12\%)$$±4%(12%)$$\pm {}^{21\%}_{18\%}$$±18%21% for EPOS-LHC, and of $$50\% (53\%)$$50%(53%)$$\pm 4\% (13\%)$$±4%(13%)$$\pm {}^{23\%}_{20\%}$$±20%23% for QGSJetII-04, is respectively needed.

Update on the Combined Analysis of Muon Measurements from Nine Air Shower Experiments

“…An update of the meta-analysis of muon measurements in EAS with energies from PeV up to tens of EeV was presented and a remarkably consistent picture is obtained after cross-calibrating the energy scales of the different experiments. The measurements agree with simulations based on the models EPOS-LHC and QGSJet-II.04, within uncertainties, up to energies of a few 10 16 eV, assuming the GSF flux model. At higher energies, an increasing excess with respect to model predictions is observed.…”

“…The z-values obtained by nine air shower experiments [4][5][6][7][8][9][10][11][12][15][16][17][18] are shown in Fig. 2.…”

“…[13,14]. This update includes new data from Auger [15] and its Underground Muon Detectors [16] (UMD), and from the IceCube Neutrino Observatory [17] (IceCube). In addition, data from the AGASA experiment [18] is included for the first time and systematic studies of the energy-dependent trend of the muon discrepancies are discussed in detail.…”

The Surface Array planned for IceCube-Gen2

“…This is already used to measure the muon density in 600 m and 800 m distance with IceTop [18]. By statistics alone these measurements can be extended in energy to several 100 PeV which will close the gap to and provide overlap with AMIGA measurements [19]. Moreover, due to the larger zenith range of in-ice coincidences, it will be possible to perform combined analyses of the TeV muons in the ice and GeV surface muons.…”

Design and implementation of the AMIGA embedded system for data acquisition

“…Two of these stations have four buried modules (two 10 m 2 modules and two 5 m 2 modules). One of these stations has eight modules (four 10 m 2 modules and four 5 m 2 modules) installed symmetrically with respect to the Auger Surface Detector; also known as a "Twin" (for validation purposes and to assess the resolution of the reconstruction procedure as described in [22]). One station has six modules (four 10 m 2 modules and two 5 m 2 modules), with the southern side of the station installed like the others, and the northern side with two 10 m 2 modules.…”