Configuration of the ATLAS trigger

The ATLAS detector at CERN's LHC will be exposed to proton-proton collisions at a nominal rate of 1 GHz from beams crossing at 40 MHz. In order to reduce the data rate to about 200 Hz, only potentially interesting events are selected by a three-level trigger system. Its first level Is Implemented In electronics and firmware whereas the higher trigger levels are based on software. To prepare the full trigger chain for the online event selection according to a certain strategy, a system Is being set up that provides the relevant configuration information, e.g., values for hardware registers in level-1 or parameters of high-level trigger algorithms - and stores the corresponding history. The same Information is used to configure the offline trigger simulation. In this presentation an overview of the ATLAS trigger system Is given concentrating on the event selection strategy and its description. The technical Implementation of the configuration system is summarized. © 2006 IEEE.