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 $3\times 10^{18}$ 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 $\sim 10^{17}$ 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 ($30^{\circ }-58^{\circ }$) 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.

Astroparticle Physics 29 (2008) 461-470

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Cited by in corpus (26)

• The Pierre Auger Cosmic Ray Observatory
• Ultrahigh Energy Cosmic Rays
• Prototype muon detectors for the AMIGA component of the Pierre Auger Observatory
• Muon Counting using Silicon Photomultipliers in the AMIGA detector of the Pierre Auger Observatory
• A new composition-sensitive parameter for Ultra-High Energy Cosmic Rays
• Design, upgrade and characterization of the silicon photomultiplier front-end for the AMIGA detector at the Pierre Auger Observatory
• A new method for reconstructing the muon lateral distribution with an array of segmented counters
• Sensitivity of the correlation between the depth of shower maximum and the muon shower size to the cosmic ray composition
• Experimental constraints on the astrophysical interpretation of the cosmic ray Galactic-extragalactic transition region
• Origin of the light cosmic ray component below the ankle
• On the design of experiments based on plastic scintillators using Geant4 simulations
• MARTA: A high-energy cosmic-ray detector concept with high-accuracy muon measurement
• Determination of the Cosmic-Ray Chemical Composition: Open Issues and Prospects
• Reconstruction of air shower muon densities using segmented counters with time resolution
• On the possibility of primary identification of individual cosmic ray showers
• Calibration of the underground muon detector of the Pierre Auger Observatory
• Design and implementation of the AMIGA embedded system for data acquisition
• A New Numerical Technique to Determine Primary Cosmic Ray Composition in the Ankle Region
• Estimation of the number of muons with muon counters
• Reconstruction of air shower muon lateral distribution functions using integrator and binary modes of underground muon detectors
• A new air-shower observable to constrain hadronic interaction models
• Composition determination of cosmic rays from the muon content of the showers
• A composition dependent energy scale and the determination of the cosmic ray primary mass in the ankle region
• A method to reconstruct the muon lateral distribution with an array of segmented counters with time resolution
• First buried muon counter prototype for the Auger Observatory
• A method to calibrate the absolute energy scale of air showers with ultra-high energy photons