When cosmic rays reach the atmosphere they found themselves in a sudden dense medium, the air of the atmosphere), and produce Extensive Air Showers (EAS).
Cosmic rays are charged particles and when they travel through a medium, such as the air in the atmosphere, they interact and lose energy. In this part, we review particles interactions, which influence the development of EAS induced by cosmic rays in the atmosphere. An air shower is a bunch of particles generated and loosing energy and desintegrating in the atmosphere, when the shower travels towards Earth's surface. We can identify three main components of these air showers: the electromagnetic component, the hadronic component, and muons and neutrinos, sometimes referred to as the muonic component. The figure below illustrates an air shower generated by a cosmic ray proton. A review paper on EAS is R. Engel, D. Tech, T. Pierog, 2011. At energies greater than 1015 eV, cosmic-ray particles can be measured only indirectly by detecting the EAS reaching detector arrays at the surface. A detailed simulation of these particle showers is needed to reconstruct the properties of the primary particles, such as energy and composition. Hence, modelig EAS is key to infer the primary particles. While electromagnetic EAS are easily understandable even based on analytical models, hadronic EAS are more complex and require QCD to be fully understood and accelerator measurements to benchmark them.
Schematics of the development of an air shower
In order to understand and model the development of an air shower, we will review the different energy loss processes as well as the target material, ie the atmosphere.
