Commissioning of a very fast track finder: the Hera-B first level trigger

In order to filter rare B decays out of the large data stream produced in the 920 GeV proton-nucleon interactions at 10 MHz in Hera-B, a very fast Track Finder has been developed, the First Level Trigger. Being Kalman filter inspired, it searches for possible particle tracks through up to seven layers of tracking chambers with a maximum latency of 10 ps. The Hera-B First Level Trigger together with the Hera-B detector was operated and commissioned during 2000. This paper describes its algorithm, implementation and the commissioning results obtained from the analysis of the collected data.