Implementation and cosmic ray test results of the Level 1 charged particle trigger for the BaBar detector

Summary form only given. The BaBar Level 1 trigger system consists of three main subsystems: the Drift Chamber Trigger, the Calorimeter Trigger and the Global Trigger. Information from the Drift Chamber and Calorimeter is processed by the respective triggers and the resulting data is sent to the Global Trigger. The algorithms of the Drift Chamber Trigger System are executed on three types of modules. First, the track segments, i.e. series of hits contiguous in space and time, are found by a set of 24 Track Segment Finder Modules (TSFM). The track segments are then linked into complete tracks by the Binary Link Tracker Module (BLTM). A set of eight PT Discriminator Modules (PTDMs) determine if the segments are consistent with tracks of particles having a transverse momentum Pt greater than a specified minimum. The Global Trigger counts tracks and attempts to match the azimuthal locations of Calorimeter towers and Drift Chamber tracks, and generates Level 1 triggers based on the results of the processing. The event production time is determined by the Global Trigger, so all the upstream components of the Level 1 Trigger form a continuously operating pipeline. This paper describes the design and implementation of the Level 1 Charged Particle Trigger System, as well as test results from Dec. 1998 to Jan. 1999 Babar cosmic test runs, including the TSF segment finding efficiency, the BLT track finding efficiency, as well as the performance of the PTD and GLT.