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

This paper describes the Second-Level Trigger for the Central Tracking Dete ctor (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 efficien cy and adequate p(T) and vertex resolution of sigma(pT) similar to 0.05 p(T )(2) (p(T) in GeV) and sigma(z-vtx) similar to 9 cm. The online performance of a highly parallel system with dynamic loading such as the CTD-SLT is ch aracterised by two quantities: the average throughput (speed) and the proce ssing time per event (latency). Detailed understanding of these quantities for the CTD-SLT derived from operational experience, simulations and a simp le model is presented. (C) 1999 Elsevier Science B.V. All rights reserved.