STAR   Computing  Simulation  
Improved SVT geometry
  Maintained by Maxim Potekhin


As reported at the Collaboration meeting in February 2003, the comparison between the experimental data on photon conversions in the STAR detector, when compared to the Monte Carlo results, indicated the presence of "extra material" in the real detector, unaccounted for in the then current GEANT model. This resulted from initial studies by Ian Johnson, further continued by other collaboration members.

It is highly desirable to rectify this situation for a variety of physics reasons.


The direct deconvolution of the "extra material" map from such studies, although tempting, is not feasible due to large systematic errors which become obvious when one takes a closer look at the problem. It was decided that instead we use these data as indicators of where to look in the physical detector (complete with all sort od technical documentations, pictured etc), in order to add the rigth materials in the right locations. This was done by myself, M.Potekhin, with the expert help from David Lynn. The following elements were identified, that were previously omitted from the model:
  • G10 printed circuit boards on each end of each ladder
  • Copper cables (high and low voltage) feeding the ladders
  • Plastic tubes feeding the coolant from the manifold to the SVT structure, and water contained therein
  • The outer shielding which features the support "cage" made of carbon composite tubes
  • The main carbon support struts which were originally described as made of Beryllium and had incorrect cross section

All of this has been added or corrected in the new version of the SVT geometry description file, svttgeo2.g. This is only activated in the version y2003b of the STAR geometry. As a reminder, y2003a is a version which contains mainly bug corrections, whereas y2003b has the aforementioned SVT improvements, plus additions in endcap calorimeter (to be done), Photon Multiplicity Detector, the FPD and other changes as well.


There have been simluations run with y2003a ("old" SVT) and y2003b ("new" SVT) geometries. As a rough metrics, plots were produced of the radiation length accrued by geantinos propagating in the detector, as a function of rapidity. It should be noted that this is more of a demonstration of principle and the physics implications may or may not be significant depending on the nature of study in question (the effects might be felt outside the apparent rapidity range covered by the added material)

Last updated by Maxim Potekhin on 9/17/2003