The Philosophy of the CORSIKA Project

The CORSIKA Monte Carlo code for the simulation of particle cascades has been used for more than 30 years by many different groups in the field of astroparticle physics. In particular, it is being used in the context of cosmic-ray physics, gamma-ray astronomy,  and high-energy neutrino detection. The original version of the code is based on Fortran and is currently available in version 7. A modern, C++-based rewrite called CORSIKA 8, is currently being developed and will also facilitate the simulation of particle cascades in dense media, in addition to air.

Both codes follow a common philosophy:

Analyzing experimental data on Extensive Air Showers (EAS) or planning corresponding experiments requires a detailed theoretical modeling of the cascade which develops when a high energy primary particle enters the atmosphere. This can only be achieved by detailed Monte Carlo calculations, taking into account all knowledge of high-energy strong and electromagnetic interactions.

Therefore, a number of computer programs has been written to simulate the development of EAS in the atmosphere and a considerable number of publications exists discussing the results of such calculations.

A common feature of all these publications is that it is difficult, if not impossible, to ascertain in detail which assumptions have been made in the programs for the interaction models, which approximations have been employed to reduce computing time, how experimental data have been converted into the unmeasured quantities required in the calculations (such as nucleus-nucleus cross sections, e.g.), etc.

This is all the more problematic, since our knowledge of high energy interactions - though much better today than in the past - is still incomplete in important features. This makes results from different groups difficult to compare, to say the least. In addition, the relevant programs are of a considerable size which - as experience shows - makes programming errors almost unavoidable, in spite of all undoubted efforts of the authors.

We therefore feel that further progress in the field of EAS simulation will only be achieved, if the groups engaged in this work make their programs available to (and, hence, checkable by) other colleagues. This procedure has been adopted in high energy physics and has proved to be very successful.

It is in the spirit of these remarks, that we describe the physics underlying the CORSIKA program developed during the last decades in Karlsruhe in our Physics Description. A complete listing of the program including all options is available from our server on request, see our download-section.

We invite all colleagues interested in EAS simulation to propose improvements, point out errors or bring forward reservations concerning assumptions or approximations which we have made. We feel that this is a necessary next step to improve our understanding of EAS.