The ATLAS TRT geometry is ready for prime time
The TRT GeoModel was completed in time for ATLAS turn-on. Dr. Taeksu Shin led a team that has completed revision of the geometry and material description (known as GeoModel) of the ATLAS TRT to match the TRT as built and installed. The GeoModel consists of a database and program holding information on the placement and material of all parts of the TRT. It has had to evolve from using the design parameters to using the final as-built values, and has also had to evolve as the rest of the ATLAS software evolved. The GeoModel is now a close representation of the ATLAS TRT, and is part of version 14 of the ATLAS software, the version that will be used for first running this year.
The top picture on the right shows the end of the TRT barrel in the final stages of installation, while the bottom picture shows a visualization of the outer parts of the computer model, with deceptive simplicity -- the model has over 300,000 components inside the surface you see.
A good match between model and reality is absolutely necessary for operation of ATLAS including inner-detector tracking software, triggering and data acquisition. The geometry description is used in event displays, and is also necessary for physics analysis and comparison of simulated data with real data.
The new model improves the accuracy of the match of component placement in the model to measurements, and the match of the material as built to the material in the model used for simulation. For most parts of the TRT, the simulation now matches the estimated as-built masses within 0.3%. It is not possible to put the complex detail of the TRT and its services in the model, so some assemblies, particularly the services (electric power, cooling, gas supplies, data cables) are modeled with a simpler volume of an appropriate mix of materials. So you can see that the complex tangle of wires and pipes in the top picture is replaced by a simple thin flat disk on the end of the TRT in the model. The active detectors are still individually modeled, but are internal to what is visible in either picture.
The plot shows the change between an earlier version of materials (blue) and the most recent (red). The big change is due to inclusion of some items in the TRT that were previously in another part of the model.