The Beginnings

Silicon detector simulation has quite some history at HEPHY. Already around the turn of the millennium, we made a simple model of charge collection in a parallel-plate capacitor configuration (1D).

That simulation was used to study the behavior of silicon detectors of various thicknesses before and after inversion due to irradiation, which was a hot topic for the CMS Tracker at that time. The results were published in Nuclear Instruments and Methods in Physics Research A 461 (2001) 192–196 .

2D Modelling with Weighting Field

In 2011, there was a debate on the effect of the Lorentz drift in a magnetic field, which should be compensated by the proper orientation of a windmill-like arrangement in the Belle II Silicon Vertex Detector. Therefore, the simulation model was extended to a 2D pattern with strips on one side, introducing the weighting field for properly calculating the charge collection.

Manual [PDF]

Thanks to this simulation, the previous orientation turned out to be wrong and thus the windmill was flipped to minimize the Lorentz deflection.

Migration to ROOT

Up to here, the simulation was coded in CVI/LabWindows which turned out to be not exactly the most suitable platform for that. Therefore, the code was ported to ROOT with a few added features like thermal diffusion. The code was made public as an open source project called “Weightfield”.

Report [PDF]

Further Developments

The project was picked up by Nicolo Cartiglia and his group at INFN Torino. They started with “Weightfield2” and over the years added more and more features, such as internal amplification or irradiation effects. The most recent version (as of 22 September 2019) is 5.0.