Commissioning ATLAS Trigger

The Large Hadron Collider (LHC) at CERN, Geneva, is now starting operation. It will ultimately provide protonproton collisions at a centre-of-mass energy of 14 TeV, a design luminosity of 10 cm−2 s−1 and a bunch-crossing rate of 40 MHz. The ATLAS collaboration has built a general purpose experiment for the LHC which is described in [1][2]. The trigger and data acquisition (T/DAQ) system must work in the challenging environment of ∼ 10 interactions per second and the large number (∼ 10) of readout channels of the ATLAS detector. The initial data stream of 1PB/s must be reduced to the ∼ 300 MB/s which can be sustained to mass storage, while efficiently retaining a maximum acceptance of physics signatures for offline analysis. To achieve this, ATLAS has designed a three-level trigger system (see Fig. 1) [3].