B-identification for Level 2: The Silicon Track Trigger at DØ

This article describes the Silicon Track Trigger (STT) which has been fully commissioned in 2004 at the DO experiment. The STT allows to enrich already at the second trigger level the data sample with events containing B mesons. The STT achieves this by providing within about 50 μ s tracks with an impact parameter resolution of around 50 μ m . The article shows preliminary results of the trigger performance and presents a fast b -identification algorithm for the second trigger level.