Geant4 is a toolkit for the simulation of the passage of particles through matter. Its areas of application include high energy, nuclear and accelerator physics, as well as studies in medical and space science. Since 2005 Zeuthen is contributing to its development and maintainence.
We implemented polarisation effects into Geant4 using the Stokes formalism to be able to simulate different polarisation dependent processes in the same way. The advantage of using the Stokes formalism is that electrons and positrons as well as photons can be treated consistantly and it is also possible to assign polarisation to media. This extension is now part of the official Geant4 release, and is used in studies of polarised beams, as well as in astro-particle application. It is constantly maintained and improved.
Bremsstrahlung and pair production are the dominating processes of high energy electromagnetic cascades, but in particular the Bremsstrahlung cross section is only known to a few percent. Therefore, and in collaboration with the CERN Geant4 group, a dedicated project of validation and improvements in these processes has been started. In a first step new high energy models derived from theory have been implemented. These include an improved treatment of matter effects like the Landau-Pomeranchuck-Migdall effect, or the Ter-Mikaelian effect. Further developments are planed, which require theoretical calculations, design of impoved Monte Carlo algorithms, and systematic validation. A proto-type of new web based validation framework for electromagnetic processes has been created, is already in use.
The validation and verification of models for hadronic interactions is a very complicated process. A huge number of different target and projectile combinations needs to be considered. The obtained cross sections are to be compared with experimental data. In order to simplify the validation process, a new software framework is currently under design. It should include an easy way to send a large number of test jobs to the grid, and compare the results with results of previous Geant4 version and with experimental data.
To measure the degree of polarisation of the produced positrons we are investigating the optimal technology for a positron polarimeter and its best location in the ILC beamline. Different options of this Low-Energy Polarimeter have been studied. A Bhabha polarimeter seems to be the best candidate. A Compton polarimeter provides an alternative after the damping ring. Detailed studies are ongoing.
The CsI crystal calorimeter for the E166 experiment was developed and produced in DESY-Zeuthen and the Experimental Particle Physics Group of the Humboldt University Berlin. A significant amount of simulation work have been done in Zeuthen. Also the main part of the analysis have been carried out in our group. The experiment is now completed, and the results were published.
A possibility to study a full-size ILC undulator module with beam is currently under investigation.
Further simulation studies concern the positron production target and the positron capture section. In Zeuthen, PPS-SIM, a framework for systematic investigation of expected positron yield and degree of polarisation was developed. This program is written C++ it utilises Geant4 for the simulation of positron production processes, polarisation transfer, and for tracking in the electromagnetic field of the first few accelerator sections. The program posseses a GUI based on Qt, and an analysis part employing the ROOT framework. It is currently used for the simulation of different positron production scenarios for ILC and CLIC.