GEANT 4 based tracking programs for CTF & BOREXINO  
Geant 4 is an object oriented simulation toolkit developed at CERN for the next generation of HEP experiments.
It has been chosen for the simulation of CTF and BOREXINO detectors, in order to meet the requirements of high flexibility, extensibility for the user and transparency of physics processes.

Geant 4 provides instruments for detector geometries definition, for tracking and transportation of particles, for different physics processes, for persistency and visualization of the generated events. The description of detector geometries in Geant 4 is based on an ISO STEP compliant solid model, this feature allows the users to import geometry description directly from CAD system and to describe any complex shape or detector deformation.

To track photons only a restricted part of the package is to be used: the geometry, the physics processes related to optical photons (reflection, refraction, absorption, etc. ), the tracking and possibly the visualization. Furthermore the absorption and reemission processes typical of our scintillator need to be added to the package.

Presently a fairly complete simulation of CTF has been written. Comparison with the CTF traditional FORTRAN code results are underway.

The tests performed up to now show that Geant 4 is well suited as a ray tracer and that, thank to C++ design, it's easily expandable introducing new processes. These conclusions are encouraging in using this tool to develop a complete Borexino/CTF tracing code.

Some pictures to enjoy!

The following pictures are produced by the Geant 4 visualization utility. Click on them to get them enlarged to their original size.

Detail of three concentrators looking at the Inner Vessel Track of a photon entering a light concentrator
Photons exiting the Inner Vessel An overall sight of the CTF detector