The TRT Fast-OR Trigger

The TRT “Fast-OR” trigger is the highest track rate cosmics trigger of the Inner Detector at ATLAS. It utilizes a fast trigger generation circuit on the front-end DTMROCs and a simple trigger logic on the TRT trigger, timing and control board. Data from the June 2009 combined run with the full Inner Detector shows a total TRT barrel trigger rate of 8 Hz on cosmics tracks with a track purity from offline reconstruction of 98%. The endcap trigger rate is ~13 Hz. Using tracks triggered by the RPC detector, the track efficiency in the barrel is estimated to 88%. The trigger “jitter” in the barrel is less than 1 clock and the total latency to the CTP is ~42 clocks. This note covers the commissioning and first use of this trigger for both TRT and ATLAS cosmic ray data taking.