A Fast Track Trigger for the H1 Collaboration

The electron–proton collider HERA will be upgraded to provide higher luminosity in the year 2001. In order to enhance the physics output especially for exclusive channels, such as open heavy quark production, a low pt Fast Track Trigger (FTT) with high resolution is built for the H1 Collaboration which reconstructs precisely all tracks measured in the central drift chamber in three-dimensions within 25 μs. Curved tracks are reconstructed down to 100 MeV in a high track multiplicity environment with a momentum resolution of better than 5%. This complex and demanding task is tackled by a highly parallel track reconstruction algorithm. The first step identifies short track segments locally with a template matching technique using FPGAs. Segment linking using the content addressable memory (CAM) functionality of the Altera APEX 20K600E and track parameter optimisation using DSPs proceed in the second step within 20 μs. Finally, the derived physics quantities such as invariant masses are computed within some hundred μs using conventional processor boards. The full design is flexible and scalable with the capability to add information from other subtrigger systems.