Extensive Air Showers and Cosmic Ray Physics above 1017eV

Mario Bertaina

doi:10.1051/epjconf/201612004002

Abstract

Cosmic Rays above 10 17 eV allow studying hadronic interactions at energies that can not be attained at accelerators yet. At the same time hadronic interaction models have to be applied to the cosmic-ray induced air-shower cascades in atmosphere to infer the nature of cosmic rays. The reliability of air-shower simulations has become the source of one of the largest systematic uncertainty in the interpretation of cosmic-ray data due to the uncertainties in modeling the hadronic interaction driving the air-shower develop- ment. This paper summarises in the first part the recent results on the cosmic ray energy spectrum, composition and anisotropy from the knee region to the GZK cutoff (1, 2) of the spectrum by means of ground-based experiments. Most of the information reported in this contribution is taken from (3-5). Aspects interconnecting cosmic ray and particle physics are reviewed in the second part of the paper.

Highlights

The cosmic ray energy spectrum above 1014 eV has a power-law like behaviour (∝ E−γ, with γ ∼ 2.7) with features which are known as the ‘knee’ at 3−4×1015 eV, where the spectrum steepens to γ ∼ 3.0, the ‘ankle’ at 2 − 8 × 1018 eV, which is characterised by a flattening of the spectrum by roughly the same change of the spectral index, i.e. back to γ ∼ 2.7, and the GZK cut-off around 5 × 1019 eV
These results show that, when indirect measurements have the opportunity of selecting almost pure beams, their findings are in reasonable agreement with direct ones and confirm a fair representation of the Extensive Air Showers (EAS) development in the atmosphere by simulation codes such as CORSIKA [18]
This difference in the data has profound consequences: the Auger data suggest that we see the maximum energy of sources, to what is observed at the knee in the cosmic ray spectrum, while the Telescope Array (TA) data suggest we observe the GZK effect

Summary

Introduction

The cosmic ray energy spectrum above 1014 eV has a power-law like behaviour (∝ E−γ, with γ ∼ 2.7) with features which are known as the ‘knee’ at 3−4×1015 eV, where the spectrum steepens to γ ∼ 3.0, the ‘ankle’ at 2 − 8 × 1018 eV, which is characterised by a flattening of the spectrum by roughly the same change of the spectral index, i.e. back to γ ∼ 2.7, and the GZK cut-off around 5 × 1019 eV. Several techniques have been employed recently on ground detectors that are sensitive to specific components of the CR radiation to overcome those uncertainties [13] Among them, it is worth mentioning the measurement of the light component (p alone, or p+He) using hadron calorimeters [14], or Cherenkov light measurements in coincidence with TeV muons [15], and RPC counters at high altitude [16]. The ARGO results allow one to cross-check the fluxes on an extended energy range (5-250 TeV) These results show that, when indirect measurements have the opportunity of selecting almost pure beams, their findings are in reasonable agreement with direct ones and confirm a fair representation of the EAS development in the atmosphere by simulation codes such as CORSIKA [18]

The knee region up to the ankle

From the ankle to the end of the spectrum

The interconnection between cosmic ray and particle physics

Conclusions