Status of the Pretrigger System for the ALICE Transition Radiation Detector ∗

1Institut für Kernphysik, Univ. Frankfurt;2GSI Helmholtzzentrum für Schwerionenforschung, Darmsta dt, Germany; 3Physikalisches Institut, Univ. Heidelberg ; 4Fachhochschule Köln The Transition Radiation Detector (TRD)[1] of the ALICE experiment at the CERN Large Hadron Collider (LHC) provides electron identification and tracking in the central barrel as well as fast triggering (6 μs). The frontend electronics (FEE) consisting of 75000 multichip modules has a total power consumption of less than 65 kW by keeping the digital electronics in a low power mode after processing each event. A fast wakeup signal for the FEE is needed to capture the TRD drift signals over the full time range and to ensure a low data processing latency. This pretrigger signal has to be generated within 400 ns after an interaction, more than 1 μs ahead of the ALICE Level0 (L0) trigger. It is based on the signals from the fast ALICE subdetectors TOF, V0 and T0, or alternatively derived from the LHC bunch counter (BC). The pretrigger system[2] consists of a number of specific hardware components (see Fig.1) which are mounted inside the L3 magnet close to the respective detectors to minimize signal propagation delays. For the TOF detector, a single field programmable gate array(FPGA), the TLMU, evaluates 576 digital bits from the entire barrel region and provides trigger signals for configurable multiplicity con ditions or geometrical correlations.