An impact parameter trigger for the DO Experiment

We describe a trigger to be used by the DO Experiment for selecting events with tracks having a large impact parameter with respect to the collision point. This device utilizes information from the Silicon Microstrip Tracker to provide improved spatial and momentum resolutions for charged particles. It is constructed or custom digital boards with programmable processors. A common motherboard provides I/O and buffer management and three different daughter boards perform the tasks of identifying the roads from the tracking trigger data, finding the clusters in the roads in the silicon detector, and fitting tracks to the clusters. This approach provides flexibility for the design, testing and maintenance phases of the project. A ∼ 60 μm impact parameter resolution is provided to the trigger framework in less than fifty microseconds. We present preliminary results from the first weeks of test run of this trigger integrated with the DO trigger system.