Cosmic rays and Extensive Air Showers
Cosmic rays are high-energy particles and atomic nuclei with energies from a few GeVs up to 10^20 eV. Today it is well established that cosmic rays interact with the atmosphere producing cascades of particles via radiative and decay processes, collectively known as Extensive Air Showers (EAS). Depending on the energy of the cosmic ray (primary), an EAS could have up to several billions of particles at the moment of its maximum development. The detailed analysis of these phenomena is highly complex, as a large number of different processes could be involved as more and more particles are produced. To properly simulate the cascade evolution and take into account all the involved physical processes and the propagation and tracking of all these secondary particles is a heavily demanding computing task.
An extensive air shower is produced during the interaction of a high-energy cosmic ray with the atmosphere. Different types of secondaries are produced: the electromagnetic component is formed by photons, electrons and positrons (in red); the muonic component is composed of muons and antimuon (green), and the hadronic component is formed by different types of mesons and baryons (in blue).
To do so, several tools have been developed, but the most extended and validated one is CORSIKA a program for the detailed simulation of extensive air showers initiated by high-energy cosmic ray particles. However, while it incorporates the possibility to select a specific atmospheric model, the values of the components of the local geomagnetic field and the altitude of the observation level, CORSIKA lacks the possibility to change those values in a dynamic way, or, most importantly, it is not possible to calculate in a direct way the secondary particles at ground produced by the integrated flux of the primary cosmic rays. These factors are significant for the calculation of the expected background radiation at any particular site around the World and under specific and time-evolving atmospheric and geomagnetic conditions.
When calculating the expected flux of secondary particles, the composition of the primary flux, the local atmospheric profile and its variations along the year, or the secular changes and the fast disturbances introduced by the Solar activity in the Earth's magnetic field have to be taken into account as they affect the number of primaries impinging the Earth's atmosphere, the evolution of the EAS in the air and the consequent flux of secondary particles at the ground.
To accomplish these tasks in a semi-autonomous way, LAGO developed ARTI, a toolkit designed to effortlessly calculate and analyze the total background flux of secondaries and the corresponding detector signals produced by the atmospheric response to the primary flux of galactic cosmic rays.