Status of the EAS studies of cosmic rays with energy below 10**16 eV

TL;DR

This paper reviews the current status of cosmic ray research below 10^16 eV using EAS experiments, discussing spectral features, composition, and the importance of hadronic interaction models, while highlighting future experimental directions.

Contribution

It provides a comprehensive summary of EAS observations, spectral irregularities, and the role of muons in understanding cosmic rays and hadronic interactions, emphasizing the need for improved models and measurements.

Findings

Observation of the knee structure in the cosmic ray spectrum

Identification of electron and positron excesses around the knee energy

Importance of muon measurements for model testing and background studies

Abstract

This paper briefly summarizes the status of the cosmic ray observations by EAS (Extended Air Shower) experiments with energy below 10**16eV and the related studies of the hadronic interaction models. Based on the observed sharp knee structure and the irregularities of the cosmic ray spectrum around knee energy, plus the newly discovered electron and positron excess, the origin of the galactic cosmic rays and the single source model interpretation are discussed, but convincing evidence is not yet available. High precision measurements of the mass composition of primary cosmic rays at knee energy will be very useful to disentangle the problem. To reach this goal, a better understanding of the hadronic interaction models is crucial. It is good to see that more dedicated accelerator and cosmic ray experiments will be conducted soon. As one EAS component, the muon distribution and muon charge ratio are important for testing the hadronic interaction models. In addition muons are an important background to neutrino experiments and all underground ultra-low background experiments. They are also a very useful tool for the meteorological studies.