Enhancing the cosmic-ray mass sensitivity of air-shower arrays by combining radio and muon detectors

Ewa M Holt,Andreas Haungs,Frank G Schröder

doi:10.1140/epjc/s10052-019-6859-4

Abstract

The muonic and electromagnetic components of air showers are sensitive to the mass of the primary cosmic particle. The sizes of the components can be measured with particle detectors on ground, and the electromagnetic component in addition indirectly via its radio emission in the atmosphere. The electromagnetic particles do not reach the ground for very inclined showers. On the contrary, the atmosphere is transparent for the radio emission and its footprint on ground increases with the zenith angle. Therefore, the radio technique offers a reliable detection over the full range of zenith angles, and in particular for inclined showers. In this work, the mass sensitivity of a combination of the radio emission with the muons is investigated in a case study for the site of the Pierre Auger Observatory using CORSIKA Monte Carlo simulations of showers in the EeV energy range. It is shown, that the radio-muon combination features superior mass separation power in particular for inclined showers, when compared to established mass observables such as a combination of muons and electrons or the shower maximum X_{mathrm{max}}. Accurate measurements of the energy-dependent mass composition of ultra-high energy cosmic rays are essential to understand their still unknown origin. Thus, the combination of muon and radio detectors can enhance the scientific performance of future air-shower arrays and offers a promising upgrade option for existing arrays.

Highlights

The development of the muonic and electromagnetic components in a cosmic-ray air shower depends on the mass of the primary particle
We studied the combination of radio and muon detection for the site of the Pierre Auger Observatory [15] in Malargüe, Argentina, where the combination of muon and radio detectors is already realized
The results shown here compare the well established mass estimator using the particles numbers with the novel method combining the muons with the radio emission

Summary

Introduction

The development of the muonic and electromagnetic components in a cosmic-ray air shower depends on the mass of the primary particle. Since air showers induced by heavier particles develop faster, the mass of the primary particle can be estimated statistically in two ways. The atmospheric depth of the shower maximum, Xmax, is on average smaller for heavier particles. Xmax can be measured best by optical and radio detectors, where the most accurate measurements of energy and Xmax are currently provided by fluorescence telescopes [5], because the systematic uncertainties are well understood. Recent radio arrays have already reached similar accuracy [6,7,8].

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Conclusion