Verhandlungen der Deutschen Physikalischen Gesellschaft, VI, vol. 40 no. T 509.8, DPG, 2005.
69. Jahrestagung der Deutschen Physikalischen Gesellschaft, Berlin, March 2005
The ATLAS experiment is being made at the Large Hadron Collider (LHC) at CERN. The LHC is a proton-proton collider with the centre of mass energy of 14 TeV. The specific of the intended physics of ATLAS is in selecting rare predicted processes with high efficiency while rejecting much higher-rate background processes over huge number of channels O(10^8). Decisions must be taken every 25 ns at the bunch-crossing rate of 40 MHz; at design luminosity (10^34cm^-2s^-1) each bunch-crossing contains about 23 inelastic pp-interactions. On the other hand, the back-end storage rate is limited to approximately 100 Hz (with the average event size of 1 MB) because of computing limitations. The ATLAS trigger system deals with the high-rate process selection by the three-stage architecture: Level1 (LVL1), Level2 (LVL2), and Event Filter (EF). The last two stages (LVL2 and EF) are called High Level Trigger (HLT). The HLT implements Steering, which is the mechanism to drive the running of certain algorithms on subsets of data as required by a sequence of steps to classify and select events. The current work on the HLT is to test the implemented prototype, particularly Steering mechanisms, and continue development of the final system.