1995 Shifted Vertex Data

Forward Tracker Group

I have looked at run 129485, this was a high statistics shifted vertex run. The Radial and Planar forward tracking chambers obtain the run T-zero by differentiating the front edge of the raw drift time distributions. In recent weeks one of the problems with this determination has been contamination by events from satellite bunches. This is also true of the shifted vertex data. The raw drift time distributions and the differentials of the front edge are available.

The degree of 'contamination' can be judged by looking at the event t-zero and z-vertex as determined by the CJC. It is clear from these that there is a large proportion of the data coming from satellite bunches. In the T-zero plot the 'normal' peak is the one near 400 ticks. There is a large satellite at 494 ticks (+20ns) and also one at 231 ticks (-60ns). The z-vertex plot shows that this leads to events at -156 cms , in addition to the shifted vertex data at +72cms.

In order to get a decent t-zero determination for the forward tracking chambers we either need to get rid of the satellite bunches altogether, or we have to use the information from the CJC on an event by event basis and reject the events in the FTD monitoring step.
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