Underground muon counters as a tool for composition analyses

Abstract

The transition energy from galactic to extragalactic cosmic ray sources is still uncertain, but it should be associated either with the region of the spectrum known as the second knee or with the ankle. The baseline design of the Pierre Auger Observatory was optimized for the highest energies. The surface array is fully efficient above 3 × 10 18 eV and, even if the hybrid mode can extend this range below 10 18 eV, the second knee and a considerable portion of the wide ankle structure are left outside its operating range. Therefore, in order to encompass these spectral features and gain further insight into the cosmic ray composition variation along the transition region, enhancements to the surface and fluorescence components of the baseline design are being implemented that will lower the full efficiency regime of the Observatory down to ∼ 10 17 eV. The surface enhancements consist of a graded infilled area of standard Auger water Cherenkov detectors deployed in two triangular grids of 433 m and 750 m of spacing. Each surface station inside this area will have an associated muon counter detector. The fluorescence enhancement, on the other hand, consists of three additional fluorescence telescopes with higher elevation angle (30 • − 58 • ) than the ones in operation at present. The aim of this paper is threefold. We study the effect of the segmentation of the muon counters and find an analytical expression to correct for the under counting due to muon pile-up. We also present a detailed method to reconstruct the muon lateral distribution function for the 750 m spacing array. Finally, we study the mass discrimination potential of a new parameter, the number of muons at 600 m from the shower axis, obtained by fitting the muon data with the above mentioned reconstruction method.

Reconstruction of air shower muon densities using segmented counters with time resolution

“…This distance is less than the average distance of the nearest detector to the shower core, which is 230 m according to Ref. [16]. More detailed simulations are currently under way to study the punch trough of electromagnetic particles.…”

“…For untriggered counters we used a Poisson likelihood, setting an upper limit to the number of muons allowed in the LDF fit as in Ref. [16]. Figure 3 shows the fit of the detector data simulated for a single shower using the profile likelihood.…”

MARTA: a high-energy cosmic-ray detector concept for high-accuracy muon measurement

“…This density is equivalent to that of muons at about 500 m from the shower axis for a proton shower with E = 10 19.5 eV and θ = 40 • . Due to the spread of the muon arrival times and the small dead time of the readout, pile-up effects become relevant only at smaller distances and the number of muons can be successfully recovered, in the case exemplified, down to about 300 m by applying dedicated algorithms [21]. For the purpose of measuring the signal very near the shower core at the highest energies, the analog channel is expected to provide counting capabilities up to 20000 particles per RPC.…”

On the design of experiments based on plastic scintillators using GEANT4 simulations

“…We have selected the plastic developed at Fermilab for our simulation setup since the extrusion method has been recently improved for MINERVA [24] and these plastics are widely used and tested in several cosmic ray experiments such the Pierre Auger Observatory [25] and BATATA [26]. It is an extruded scintillator with a co-extruded reflective coating, whose manufacturing process has been optimized for higher light yield and lower costs.…”