The H1 trigger with emphasis on tracking triggers

Since the commissioning of the electron proton collider HERA in 1992 at DESY the H1 experiment collected data with stable performance. The collision frequency of 10.4 MHz necessitates a pipelined design of the data acquisition and the trigger. A multilevel trigger is used to provide the required selectivity on physics processes and to allow for fast rejection of background events. Subdetector-based, deadtime-free triggers are combined to produce a first level trigger. The dcr φ trigger described herein, extracts its data from the central driftchamber. The drifttime of the signals is measured online and logical functions are applied on the digitized time measurements. To account for different performance parameters of the driftchamber the hardware demands a high flexibility, thus leading to a design with Programmable Gate Arrays (XILINX). Track-finding is achieved by means of ten thousand look-up tables, each with typically 20 inputs. Although the signals for one event will arrive within 1.1 μs , it is possible to determine the timing of the event online within one bunchcrossing (0.096 μs ).