The vertex finding technique is based on the grouping technique. Points on each SVT layer are clustered in groups of 3 assuming a primary vertex position. When the correct vertex location is identified there will be a peak in the number of groups. This method only works for finding the Z coordinate.

Some preliminary results can be seen below. Low density cocktail events have been used and the primary vertex location found using the SVT hit grouping technique and the TPC tracking. The difference in the coordinate is plotted and gives soome idea of the resolution. The second plot shows the GEANT actual vertex position - the found SVT location. You can see the resolution is good to a few hundred microns. I believe with some study this could possibly be made better as the binning is still reasonably crude when the fit is done to find the Z value.

The resolution between the two techniques is, I think, good enough that we can monitor the "alignment" between the two detectors using this study. This could move due to drift veloicities changing due to temperature or pressure changes.

A similar technique can be used to find primary tracks see here See reference below for more details: Star notes of interest:

Helen L. Caines
Last modified: Tue Apr 24 12:13:35 EDT 2001