What is Geant4?

Geant4 is a C++ set of libraries designed for Monte-Carlo simultation. Initially developped at CERN for high energy physics purpose, this geometry and tracking toolkit contains a large amount of data about particles, interactions and materials.

In order to build a simple simulation, one just has to define a geometry and the interactions to consider. For non trivial experiments like LE$\mu$SR , one may have to personalize some aspects of the original Geant4 code like physics processes or electromagnetic fields. It is now widely used in all kind of fields from dna modelling to astrophysics.

The simulation can be interactive thanks to a user interface already included in Geant4. The possibilities of geometry visualization and histogramming are key elements of Geant4.