The design and performance of the ZEUS central tracking detector second-level trigger

This paper describes the Second-Level Trigger for the Central Tracking Detector (CTD-SLT) of the ZEUS experiment. The CTD-SLT consists of a network of micro-processors running a track finding algorithm. Operational experience gained during the 1995–1997 HERA data taking periods show that the maximum processing rate approaches 800 Hz, with almost 100% track finding efficiency and adequate pT and vertex resolution of σpT∼0.05 p2T (pT in GeV) and σz−vtx∼9 cm. The online performance of a highly parallel system with dynamic loading such as the CTD-SLT is characterised by two quantities: the average throughput (speed) and the processing time per event (latency). Detailed understanding of these quantities for the CTD-SLT derived from operational experience, simulations and a simple model is presented.