Extensive Air Showers and Hadronic Interactions at High Energy

At energies greater than 10¹⁵ eV, cosmic-ray particles can be measured only indirectly by detecting the extensive showers of secondary particles they create in the Earth's atmosphere. A detailed simulation of these particle showers is needed to reconstruct the properties of the primary particles. Key to understanding extensive air showers is the modeling of hadronic multiparticle production at energies from the particle-production threshold up to 10²⁰ eV—far beyond the reach of man-made accelerators. In this article, we introduce the relation between extensive air showers and hadronic interactions at high energy. We review air shower predictions of commonly used interaction models and discuss their uncertainties. Finally, we illustrate the importance of accelerator measurements for air shower simulation and, complementarily, the information that can be obtained from air showers on particle production.